Handle streams in base module stream
A base module's stream (the platform for RHEL) could have Z-stream suffix, e.g.
el8.0.0.z, this patch handles this Z-stream suffix and other potential streams
by returning the stream version as a float with configured suffix value. For
example, el8.1.0.z would be parsed as 080100.1. Note that, the 0.1 is totally
configured in config and it actually could be any value according to concrete
cases in practice.
Config STREAM_SUFFIXES is enabled in TestConfiguration so that tests depending
on the return value from ModuleBuild.get_stream_version are covered.
Part fixture of test TestMMDResolver.test_solve_virtual_streams is updated by
adding Z-stream suffix to platform:el8.2.0 in order to ensure this patch does
not break the MMD resolver.
Addresses FACTORY-4307
Signed-off-by: Chenxiong Qi <cqi@redhat.com>