maas i386/*18.04* images fail to successfully deploy with maas 3.1

Yesterday some of the i386 deployments for kernel tests failed. There appears to be an issue with the maas images that only affects i386/18.04.

The issue may have existed a lot longer, since we were using some alternative means to deploy i386/18.04 on our test machines.

See the attached logs
I have begun to triage this problem and feel it could be related to the boot-initrd generated for i386/bionic. I will update the bug as I find more information.

The Attached Logs are from a deployment of i386/18.04-hwe-edge

[ 6.667640] Write protecting kernel text and read-only data: 18368k
[ 6.674760] NX-protecting the kernel data: 12532k
[ 6.680638] x86/mm: Checked W+X mappings: passed, no W+X pages found.
[ 6.688010] x86/mm: Checking user space page tables
[ 6.693642] x86/mm: Checked W+X mappings: passed, no W+X pages found.
[ 6.700945] Run /init as init process
[ 6.705199] Failed to execute /init (error -2)
[ 6.710267] Run /sbin/init as init process
[ 6.714961] Run /etc/init as init process
[ 6.719552] Run /bin/init as init process
[ 6.724136] Run /bin/sh as init process
[ 6.728529] Kernel panic - not syncing: No working init found. Try passing init= option to kernel. See Linux Documentation/admin-guide/init.rst for guidance.
[ 6.744519] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.4.0-109-generic #123~18.04.1-Ubuntu
[ 6.753976] Hardware name: Dell Inc. PowerEdge R320/0DY523, BIOS 1.2.4 05/11/2012
[ 6.762462] Call Trace:
[ 6.765297] dump_stack+0x60/0x7a
[ 6.769097] ? __noinstr_text_end+0x2a00/0x2a10
[ 6.774257] panic+0xa8/0x26f
[ 6.777669] ? rest_init+0xa0/0xa0
[ 6.781568] kernel_init+0xee/0x100
[ 6.785565] ret_from_fork+0x2e/0x38
[ 6.789696] Kernel Offset: 0x15000000 from 0xc1000000 (relocation range: 0xc0000000-0xf7dfdfff)
[ 6.803177] ---[ end Kernel panic - not syncing: No working init found. Try passing init= option to kernel. See Linux Documentation/admin-guide/init.rst for guidance. ]--

ii maas 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all "Metal as a Service" is a physical cloud and IPAM
ii maas-cli 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all MAAS client and command-line interface
ii maas-common 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all MAAS server common files
ii maas-dhcp 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all MAAS DHCP server
ii maas-proxy 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all MAAS Caching Proxy
ii maas-rack-controller 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all Rack Controller for MAAS
ii maas-region-api 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all Region controller API service for MAAS
ii maas-region-controller 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all Region Controller for MAAS
ii python3-django-maas 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all MAAS server Django web framework (Python 3)
ii python3-maas-client 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all MAAS python API client (Python 3)
ii python3-maas-provisioningserver 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all MAAS server provisioning libraries (Python 3)

ubuntu@maas2:~$ dpkg -l | grep curtin
ii curtin-common 21.3-1004-g8c131399-0ubuntu1+307~trunk~ubuntu20.04.1 all Library and tools for curtin installer
ii python3-curtin 21.3-1004-g8c131399-0ubuntu1+307~trunk~ubuntu20.04.1 all Library and tools for curtin installer

$ sudo apt-cache policy curtin-common
curtin-common:
  Installed: 21.3-1004-g8c131399-0ubuntu1+307~trunk~ubuntu20.04.1
  Candidate: 21.3-1004-g8c131399-0ubuntu1+307~trunk~ubuntu20.04.1
  Version table:
 *** 21.3-1004-g8c131399-0ubuntu1+307~trunk~ubuntu20.04.1 500
        500 http://ppa.launchpad.net/curtin-dev/daily/ubuntu focal/main amd64 Packages
        100 /var/lib/dpkg/status
     21.3-0ubuntu1~20.04.1 500
        500 http://ppa.launchpad.net/maas/3.1/ubuntu focal/main amd64 Packages
        500 http://ppa.launchpad.net/maas/3.2/ubuntu focal/main amd64 Packages
     21.2-0ubuntu1~20.04.1 500
        500 http://ppa.launchpad.net/maas/2.9/ubuntu focal/main amd64 Packages
     20.1-2-g42a9667f-0ubuntu1~20.04.1 500
        500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
     19.3-27-g437caaa9-0ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages