download_mirror.sh failure when not run with -n

[Scott Little]

Brief Description
-----------------
download_mirror.sh fails when following the layered build instructions.
In those instructions, the '-n' flag is not specified. Successful download
should still be possible with without the '-n' flag.

Note: Build servers do use '-n', so the problem has been undetected until recently.

Severity
--------
Critical: StarlingX fails to build

Steps to Reproduce
------------------
Set up a layered build environment.
cd $MY_REPO_ROOT_DIR/stx-tools/centos-mirror-tools
./download_mirror.sh

Expected Behavior
------------------
All packages download

Actual Behavior
----------------
rpms that use the yumdownloader method fail to download

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

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

Branch/Pull Time/Commit
-----------------------
July 1, 2022

Last Pass
---------
Unknown

Timestamp/Logs
--------------
[Errno 13] Permission denied: '/var/lib/rpm/.dbenv.lock'

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

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

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/tools/+/848655

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/tools/+/848655
Committed: https://opendev.org/starlingx/tools/commit/5f8fc4e7b3e0fea7bc1e7918a2b914fd153e7baf
Submitter: "Zuul (22348)"
Branch: master

commit 5f8fc4e7b3e0fea7bc1e7918a2b914fd153e7baf
Author: Scott Little <email address hidden>
Date: Mon Jul 4 12:56:06 2022 -0400

    Fix download_mirror.sh without -n

    download_mirror.sh fails when run without '-n'.

    It seems that some functions were relocated to utils.sh that
    require the 'SUDO' variable to be defined. Those common utilities
    are called from both download_mirror.sh and dl_rpms.sh.

    download_mirror.sh sets it correctly, but dl_rpms.sh does not.
    Instead dl_rpms.sh is setting 'SUDOCMD', which the utils.sh ignores.
    The result is that some yum commands are runs under sudo, while others
    are not. Eventually yumdownloader failes with ...

       Permission denied: '/var/lib/rpm/.dbenv.lock'

    The fix is to convert dl_rpms.sh to use SUDO rather than SUDOCMD.

    Closes-Bug: 1980684
    Signed-off-by: Scott Little <email address hidden>
    Change-Id: Ib4afdba0260e67f06997c360272f40f28fb11834