FAB-15300 Consensus migration: integ. test extended

Cover the functionality introduced my the migration filter.
Test proper rejection of forbidden transitions when executing
consensus type migration.

Some code hygiene as well.

Change-Id: I8399453a5d63f39de388863ebbcb9c3d8dc5a435
Signed-off-by: Yoav Tock <tock@il.ibm.com>

Author: tock-ibm