CentOS 6 deployment fails to deploy with Bionic

* Operating system: Ubuntu 18.04
* MAAS version: 2.4.0 (6981-g011e51b7a-0ubuntu1~18.04.1)

root@maas1:~# ls -lah /var/log/maas/
total 16M
drwxr-xr-x 4 maas maas 4.0K May 23 06:25 .
drwxrwxr-x 18 root syslog 4.0K Jun 6 06:25 ..
-rw-r--r-- 1 syslog syslog 932K Jun 6 15:41 maas.log
drwxr-x--- 2 proxy proxy 4.0K Jun 6 06:25 proxy
-rw-r--r-- 1 maas maas 5.0M Jun 6 15:42 rackd.log
-rw-r--r-- 1 maas maas 9.3M Jun 6 15:49 regiond.log
-rw-r--r-- 1 maas maas 391K May 23 06:24 regiond.log.1.gz
drwxr-xr-x 6 syslog syslog 4.0K May 31 13:56 rsyslog

# dpkg -l '*maas*'|cat
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-===============================-======================================-============-=================================================
ii maas 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all "Metal as a Service" is a physical cloud and IPAM
ii maas-cli 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all MAAS client and command-line interface
un maas-cluster-controller <none> <none> (no description available)
ii maas-common 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all MAAS server common files
ii maas-dhcp 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all MAAS DHCP server
un maas-dns <none> <none> (no description available)
ii maas-proxy 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all MAAS Caching Proxy
ii maas-rack-controller 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all Rack Controller for MAAS
ii maas-region-api 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all Region controller API service for MAAS
ii maas-region-controller 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all Region Controller for MAAS
un maas-region-controller-min <none> <none> (no description available)
un python-django-maas <none> <none> (no description available)
un python-maas-client <none> <none> (no description available)
un python-maas-provisioningserver <none> <none> (no description available)
ii python3-django-maas 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all MAAS server Django web framework (Python 3)
ii python3-maas-client 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all MAAS python API client (Python 3)
ii python3-maas-provisioningserver 2.4.0-6981-g011e51b7a-0ubuntu1~18.04.1 all MAAS server provisioning libraries (Python 3)

I'm running into an issue related to CentOS 6 deployments failing with multiple MAAS installations using different network configurations (one simple and one complex) for the machines being deployed. I thought it might have been related to the complex network config however I've confirmed the same problem exists with what I would consider a simple network config. Below is the error output found in the installation log once the CentOS 6 deployment fails:

----------------------------------------------------------------------------------

Traceback (most recent call last):

  File "/tmp/tmpzkdjc8hq/target/curtin/curtin-hooks.py", line 393, in <module>

    main()

  File "/tmp/tmpzkdjc8hq/target/curtin/curtin-hooks.py", line 376, in main

    grub_root = get_grub_root(target)

  File "/tmp/tmpzkdjc8hq/target/curtin/curtin-hooks.py", line 208, in get_grub_root

    return regex.groups()[0]

AttributeError: 'NoneType' object has no attribute 'groups'

Unexpected error while running command.

Command: ['/tmp/tmpzkdjc8hq/target/curtin/curtin-hooks']

Exit code: 1

Reason: -

Stdout: ''

Stderr: ''

curtin: Installation failed with exception: Unexpected error while running command.

Command: ['curtin', 'curthooks']

Exit code: 3

Reason: -

Stdout: Traceback (most recent call last):

          File "/tmp/tmpzkdjc8hq/target/curtin/curtin-hooks.py", line 393, in <module>

            main()

          File "/tmp/tmpzkdjc8hq/target/curtin/curtin-hooks.py", line 376, in main

            grub_root = get_grub_root(target)

          File "/tmp/tmpzkdjc8hq/target/curtin/curtin-hooks.py", line 208, in get_grub_root

            return regex.groups()[0]

        AttributeError: 'NoneType' object has no attribute 'groups'

        Unexpected error while running command.

        Command: ['/tmp/tmpzkdjc8hq/target/curtin/curtin-hooks']

        Exit code: 1

        Reason: -

        Stdout: ''

        Stderr: ''

Stderr: ''

----------------------------------------------------------------------------------

Here are the steps to recreate the problem:

1.) Enlist the server into MAAS and rename it to the appropriate server name
2.) Mark the machine as broken and configure the network interfaces as follows:
    - eth0 - private subnet used for MAAS deployments
    - eth1 - public /29 subnet dedicated to specific server (gateway to internet here)
3.) Mark the machine as fixed and then commission the machine ensuring to select the commissioning option to retain the current network config
4.) Once the server has been successfully commissioned, acquire the server (admin user) and deploy with CentOS 6.
5.) The server indicates the installation has begun and CentOS 6 cloud installer image is downloaded for install/extraction however the error listed above is produced immediately after the image download then the status changes to 'Failed Deployment'

I have no problems successfully installing via MAAS operating systems Ubuntu 14.04, Ubuntu 16.04, Ubuntu 18.04 and CentOS 7 using the same exact steps listed above.

If you need any additional information or have any questions please let me know and I'll be happy to oblige.

Thanks!