build-docker-images: --only option doesn't work correctly

[Davlet Panech]

Brief Description
-----------------

The option "--only" of build-stx-images.sh doesn't work correctly. The root cause is missing shell quotes in function find_image_build_files, which causes this filter to falsely match projects that don't define PROJECT or LABEL in some cases.

Severity
--------
Major

Steps to Reproduce
------------------
Pass the same image name to --only twice:

build-stx-images.sh --only stx-audit,stx-audit [...]

Expected Behavior
------------------
Only the specified images should be built

Actual Behavior
----------------
Script builds many other images besides the specified one(s)

Reproducibility
---------------
Reproducible

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

Branch/Pull Time/Commit
-----------------------
master/2022-06-07

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

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

Test Activity
-------------
N/A

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

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/root/+/845027

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/root/+/845027
Committed: https://opendev.org/starlingx/root/commit/e712f134b9eeeae0164ceca0ca930420cbcc14cd
Submitter: "Zuul (22348)"
Branch: master

commit e712f134b9eeeae0164ceca0ca930420cbcc14cd
Author: Davlet Panech <email address hidden>
Date: Tue Jun 7 15:21:16 2022 -0400

    build-stx-images.sh: proper shell quoting

    The "--only" parameter doesn't work properly in some circumstances and
    builds more images than requested. Solution: add shell quotes.

    TESTS
    ===================================

    Run build-stx-images.sh --only stx-audit,stx-audit [...]
    and make sure it builds only the requested image.

    Closes-Bug: 1977879
    Signed-off-by: Davlet Panech <email address hidden>
    Change-Id: I4c9ddb16dd5e447c38d29e442f4e6790e5d146bb