qa_openstack: Allow /dev/xvdX for cinder/manila block devs
qa_openstack: Allow /dev/xvdX for cinder/manila block devs

When qa_openstack runs under a Xen hypervisor, the block device names
may start with /dev/xvd so also check for available devices there.

SUSE-Cloud/automation,aspiers/automation,SUSE-Cloud/automation,gosipyan/automation,SUSE-Cloud/automation,gosipyan/automation,aspiers/automation,vmoravec/automation,gosipyan/automation,gosipyan/automation,vmoravec/automation,aspiers/automation,vmoravec/automation,SUSE-Cloud/automation,aspiers/automation,vmoravec/automation