ec2: Fix bug with running/stopped state and wait=yes.

If `get_all_instances` returns multiple reservations, the old wait loop only
dealt with the first reservation. Thus, the wait loop may end before all
instances get to be running/stopped.

Also clean up the code a little.
Merge branch 'ec2-start-stop' of https://github.com/sayap/ansible into sayap-ec2-start-stop
Merge branch 'sayap-ec2-start-stop' into devel