CI: Modifications to enable reproducible builds

Added default source revision file name to common.py.
Modified the integration_into_manifest function to set the
corresponding subproject hash in the SRCREV.conf file if the
repository is not found in the default.xml file. The
merge_into_manifest function now works even if the names of
the master branches in the manifest and in the project
repository are different.

BCS 746-000016