Generate CA Certificates that are valid for a bit further back in time.

See bug #1352944. We were generating certificates that were valid 5 minutes ago, to avoid
problems with the clock on the client being out of sync with the clock on the server, but
it seems 5 minutes isn't quite enough to account for real world clock skew. So bump it
up to 1 week.
add some comments about what we are testing.

Also, do the same work for Server and Client certs as well as the CA cert.
Merge pull request #601 from jameinel/week-old-certs-1352944

Generate CA Certificates that are valid for a bit further back in time (bug #1352944).

See bug #1352944. We were generating certificates that were valid 5 minutes ago, to avoid
problems with the clock on the client being out of sync with the clock on the server, but
it seems 5 minutes isn't quite enough to account for real world clock skew. So bump it
up to 1 week.