MigrationRunner.get_current_revision() was creating a SQLite engine without
connect_args={'check_same_thread': False}, causing ProgrammingError when called
from a different thread than the one that created the engine. This is now
consistent with init_or_upgrade() which correctly passes check_same_thread=False
for all SQLite engines.
Added a Behave scenario to verify that get_current_revision() passes
check_same_thread=False when creating a SQLite engine.
ISSUES CLOSED: #10952
HAL9000