Failure to copy correct layer specific mock.cfg.proto

[Scott Little]

Brief Description
-----------------
One of the jobs of generate-centos-repo.sh is to copy the correct mock.cfg*proto file
into centos-repo. If a layer argument is provided, it should look for a layer specific
version of this file, and only fall back on the default file if a layer specific file
is not found.

The current implementation always selects the default file.

Severity
--------
Minor:

Steps to Reproduce
------------------
generate-centos-repo.sh --layer=distro
ls -al $MY_REPO/centos-repo/mock.cfg*proto

Expected Behavior
------------------
The layer specific 'mock.cfg.distro.proto' is copied into $MY_REPO/centos-repo/

Actual Behavior
----------------
The default 'mock.cfg.proto' is copied into $MY_REPO/centos-repo/

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

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

Branch/Pull Time/Commit
-----------------------
N/A

Last Pass
---------
N/A

Timestamp/Logs
--------------
N/A

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

Workaround
----------
N/A

[Scott Little (slittle1)]

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