* Relax diff on maintenance_policy.daily_maintenance_window.start_time
If the maintenance window has been set outside of Terraform to a time with a
single-digit hour (such as 1:00), and the terraform definition is set to the
same hour but with a leading zero as per validation (i.e. 01:00), do not
consider the time to be changed (as we currently don't support update on this
property).
Fixes#719
* Generalise rfc3339TimeDiffSuppress and add more test cases