1) Add config for the container layer.
2) Add support for the new config file 'required_layer_wheel_inc.cfg',
Which will specify the default urls for lower layer wheels.inc files.
These files must be downloaded by download_mirror.sh, and linked by
generate-cgcs-centos-repo.sh.
3) Add options to download_mirror.sh and generate-cgcs-centos-repo.sh
allowing overrides or additions to the set of url's for lower layer
wheels.inc
4) Changes to allow build scripts running within a docker container
to launch a sister (not daughter) container. This will allow
build-wheels to run within a container.
Story: 2006166
Task: 38980
Depends-On: https://review.opendev.org/711773
Depends-On: https://review.opendev.org/717755
Change-Id: I95c71a0327dc9d919ed835d3661a6f1ec7ce30c7
Signed-off-by: Scott Little <scott.little@windriver.com>
f6755e179a