Verify created/updated timestamps are isotime

We format these timestamps using timeutils.isotime() in the server
view builder, so we should check that in the API sample tests rather
than using the generic timestamp regexp.

Full context here:

  http://lists.openstack.org/pipermail/openstack-dev/2014-April/033971.html

Change-Id: Id55f13d8163249275220151dd88c67b47e6176c9
Merge "Verify created/updated timestamps are isotime"