Fix incorrect test_group in zull job definition
Fix incorrect test_group in zull job definition

Both of mysql trove-scenario jobs performed the same tests
group (mysql-supported-single).

This change sets correct group for trove-scenario-mysql-multi job.

Furthermore, to be consistent, trove_test_datastore has been passed
explicite for trove-scenario-mysql-single job.

Change-Id: I377e17ebf690c79d1c369116697177f992b3df65
Signed-off-by: Marcin Piwowarczyk <82f77c3faa2d9bd1e8b9270de3963c7aed2ed46e@samsung.com>

openstack/trove,openstack/trove