Fix broken baremetal migration tests

Change 1c5518ba introduced different user/passwd for the baremetal CI
tests, which did not match the CI systems. Since then, all the baremetal
migration tests have been skipped or failing.

This patch sets the user/passwd back to 'openstack_citest'.

Change-Id: I88508d83d6e9e63f20c26704ec6b455c48a33e8f