In case /var/lib/nova/instances resides on NFS we have seen migrations
failing with 'Failed to get "write" lock - Is another process using the
image' errors.
This has been tracked down to grace/lease timeouts not having expired
before attempting the migration/evacuate, so in this cases it might be
desirable to delay the nova evacuate call to give the storage time to
release the locks.
Change-Id: Ie2fe784202d754eda38092479b1ab3ff4d02136a
Resolves: rhbz#1740069
8b9c49fd96