Add some OpenStack support.

I found that in the cloud I tried, by the time this script runs, there
is no default route in effect yet. That takes some 5 to 10 seconds
longer. So I added a retry loop, and to make that easier, changed the
order of queries.  To make sure it doesn't wait ~forever for a
non-existent service I added the -q 1 option to ftp invocations.

I also added OpenStack-specific metadata which contains a different
random_seed of 512 bytes every time it is requested.  See
https://github.com/openstack/nova/blob/master/nova/api/metadata/base.py#L355
It may not be trusted data but only in the strictest sense of the word.
The data can only be observed by people with access to the cloud's
overlay network for the particular VM.

(rhialto)