openonuAdapterGo: OMCI extended message set - test support of MIB upload

A new test (suite or case) has to be implemented to test the following scenario:

• start voltha with BBSIM supporting OMCI baseline message set (EXTRA_HELM_FLAGS=" --set omccVersion=163)
• bring-up BBSIM-ONU
• measure and save the time until "initial_mib_downloaded" is reached
• save resulting MIB template and delete it from kv-store
• restart BBSIM supporting OMCI extended message set (EXTRA_HELM_FLAGS=" --set omccVersion=180)
• bring-up BBSIM-ONU
• measure and save the time until "initial_mib_downloaded" is reached
• save resulting MIB template from kv-store
• compare the saved MIB-templates - should be identical
• compare the time values of the two tests - the test with the extended message set should reach the state much faster