clean up the migrator tests
more refactoring of the migration test
Merge remote-tracking branch 'origin/1.10' into 1.12

Conflicts:
	core/test-api/db/src/test/java/org/opennms/core/test/db/MigratorTest.java
Merge remote-tracking branch 'opennms/1.12'

Conflicts:
	core/test-api/db/src/test/java/org/opennms/core/test/db/MigratorTest.java
	core/test-api/lib/src/main/java/org/opennms/core/test/MockLogAppender.java