Nova evacuate failed when VM is in SHUTOFF status

When the VM is in SHUTOFF status and the original compute host is
down, issue the "nova evacuate" command to rebuild the VM on
another host, it is failed due to a type error: string indices
must be integers.

Fix bug 1176773
Change-Id: I76ebce6882198365717167f29a484e4ec994db0c
(cherry picked from commit 2c1bd79a202c868bfeee7ca92e817ad19ef06b76)
Merge "Nova evacuate failed when VM is in SHUTOFF status" into stable/grizzly