Allow updating services when quota is almost reached

The MaxServiceInstancePolicy assumes that all requests are to create a
service instance, and therefore checks whether the quota is less than
the quota, rather than <=. This is a problem when you're exactly at the
quota limit and try to, for example, rename a service instance. You get
a message saying you've exceeded your quota, which you haven't.
Merge remote-tracking branch 'origin/pr/210'
User provided instances dont count towards quota