Catching InstanceNotFound exception during reboot instance

If the instance is deleted during reboot(most of soft reboot), an
InstanceNotFound exception may be raised when update instance info to DB,
and the instance may become running deleted, so catching the exception and
logging it.
This commit is a supplement of bug #1111213, which may result in the instance
becomes running deleted, when deleting an instance after soft reboot.

Change-Id: I3e8df109d431040c64e87f16ca84ff5b62dde898
Merge "Catching InstanceNotFound exception during reboot instance"