Build failure due to use of centos 8 mock cfg in a centos 7 conainer

[Scott Little]

Brief Description
-----------------
Build fails in Centos 7 build environments.

We are incorrectly trying to use a centos 8 mock configuration
in a centos 7 build container.

The problem was traced to the interaction of two bugs, one each in
https://review.opendev.org/c/starlingx/tools/+/762700
and
https://review.opendev.org/c/starlingx/root/+/762701

Severity
--------
Critical: Can't build

Steps to Reproduce
------------------
generate-cgcs-centos-repo.sh
populate_downloads.sh
build-pkgs

Expected Behavior
------------------
build passes

Actual Behavior
----------------
build failes

Reproducibility
---------------
100%

System Configuration
--------------------
N/A

Branch/Pull Time/Commit
-----------------------
Dec 1, 2020
https://review.opendev.org/c/starlingx/tools/+/762700
https://review.opendev.org/c/starlingx/root/+/762701

Last Pass
---------
Nov 30 2020

Timestamp/Logs
--------------
03:42:56 INFO: mock.py version 1.4.16 starting (python version = 3.6.8)...
03:42:56 ERROR: EOF when reading a line
03:42:56 Traceback (most recent call last):
03:42:56 File "/usr/libexec/mock/mock", line 977, in <module>
03:42:56 main()
03:42:56 File "/usr/lib/python3.6/site-packages/mockbuild/trace_decorator.py", line 96, in trace
03:42:56 result = func(*args, **kw)
03:42:56 File "/usr/libexec/mock/mock", line 730, in main
03:42:56 buildroot = Buildroot(config_opts, uidManager, state, plugins, bootstrap_buildroot)
03:42:56 File "/usr/lib/python3.6/site-packages/mockbuild/trace_decorator.py", line 96, in trace
03:42:56 result = func(*args, **kw)
03:42:56 File "/usr/lib/python3.6/site-packages/mockbuild/buildroot.py", line 62, in __init__
03:42:56 self.pkg_manager = package_manager(config, self, plugins, bootstrap_buildroot)
03:42:56 File "/usr/lib/python3.6/site-packages/mockbuild/package_manager.py", line 44, in package_manager
03:42:56 input("Press Enter to continue.")
03:42:56 EOFError: EOF when reading a line

Test Activity
-------------
Build

Workaround
----------
revert the two updates above

[Ghada Khalil (gkhalil)]

stx.5.0 / critical - build failure

[Scott Little (slittle1)]

Fixed by https://review.opendev.org/c/starlingx/tools/+/765828

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: f/centos8
Review: https://review.opendev.org/c/starlingx/tools/+/786141

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/tools/+/786141
Committed: https://opendev.org/starlingx/tools/commit/82cb355f7f4a18ca1375709747ca5923f374ec26
Submitter: "Zuul (22348)"
Branch: f/centos8

commit 82cb355f7f4a18ca1375709747ca5923f374ec26
Author: Scott Little <email address hidden>
Date: Wed Dec 2 12:08:27 2020 -0500

    Fix selection of release specific mock prototype

    Commit https://review.opendev.org/c/starlingx/root/+/762700
    was intended to include the code to select the release specific
    mock config prototype.

        e.g. mock.cfg.centos7.proto

    As delivered, it would always select the default.

        e.g. mock.cfg.proto

    Other improvements:
    - remove some trailing whitespace
    - improved cleanup of temorary directories

    Closes-Bug: 1906547
    Signed-off-by: Scott Little <email address hidden>
    (cherry picked from commit 451b9513e4d224d47e3d4d2d543e1bc834b78794)
    Change-Id: Idd307e60c266716a0a7f3beebf0a05b4a8ad37d5

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: f/centos8
Review: https://review.opendev.org/c/starlingx/tools/+/792229

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Chuck Short <email address hidden>" on branch: f/centos8
Review: https://review.opendev.org/c/starlingx/tools/+/792229
Reason: Updated merge coming

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: f/centos8
Review: https://review.opendev.org/c/starlingx/tools/+/793627