Allow proper instance with volume suspension

When suspending a stack that contains an instance with a volume
attached through the instance's "Volumes" property, the stack will
go into a SUSPEND_COMPLETE state, but the actual instance will still
be in an ACTIVE state. This is because check_suspend_complete will
return TRUE without ever starting the instance's suspend task.
This commit ensures that the instance suspension TaskRunner is
actually started.

Change-Id: I77291d21b291242684cf42e7143b264521ba113e
Closes-Bug: #1284306
Merge "Allow proper instance with volume suspension"