quickstart fails with http_proxy

Description:

When deploying tripleo using quickstart (current master) on a node behind an http_proxy, the install fails when attempting to install packages in the overcloud image using guestfish.
NOTE: This is related but a bit different to https://bugs.launchpad.net/bugs/1686353 since yum package installs on the node prior to the virt-customize succeed.

Steps to reproduce:

Setup physical node behind http proxy. Configure node with /etc/environment variables for accessing the proxy:

Run the following with the node as the VIRTHOST
bash quickstart.sh -R master --no-clone --tags all --nodes config/nodes/1ctlr_1comp.yml --clean $VIRTHOST

Expected result:
Install should work

Actual Result:
Install fails.

Following error is given:

TASK [modify-image : Run virt-customize on the provided image] ************************************************************************************************************************************
task path: /root/.quickstart/usr/local/share/ansible/roles/modify-image/tasks/libguestfs.yml:40
Tuesday 05 December 2017 17:22:50 +0200 (0:00:00.044) 0:43:23.739 ******
fatal: [172.25.87.11]: FAILED! => {"changed": true, "cmd": "virt-customize --run /home/stack/repo_setup.sh -a /home/stack/overcloud-full.qcow2 > /home/stack/_home_stack_repo_setup.sh.log 2>&1", "delta": "0:10:07.825112", "end": "2017-12-05 07:38:46.050571", "failed": true, "msg": "non-zero return code", "rc": 1, "start": "2017-12-05 07:28:38.225459", "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}

Logs:
The setup.sh.log file shows the following issues:
failure: repodata/repomd.xml from delorean-queens-testing: [Errno 256] No more mirrors to try.
https://trunk.rdoproject.org/centos7-master/deps/el7/repodata/repomd.xml: [Errno 12] Timeout on https://trunk.rdoproject.org/centos7-master/deps/el7/repodata/repomd.xml: (28, 'Connection timed out after 30001 milliseconds')
virt-customize: error: /home/stack/repo_setup.sh: command exited with an
error

Running the same virt-customize command, from the shell, which has the env variable (export LIBGUESTFS_BACKEND=direct) set, appears to work ok.

It appears that the ansible script needs to pass this env variable.