Allow reserved status for attach check
Allow reserved status for attach check

This issue was due to Nova changes it's volume attach workflow
(https://review.openstack.org/#/c/330285) which allows `reserved`
status.
Closes-Bug: #1737343

Change-Id: I13f1906f53a89586bb51c0b70fa768a9500dfa26

noironetworks/heat,openstack/heat,noironetworks/heat,openstack/heat