Add ServiceInstanceProvider to service protobufs
Add ServiceInstanceProvider to service protobufs

This commit adds a 'provider' to a ServiceInstance, this is needed
so clients can figure out what the correct way of contacting the
service.  The 'servers' should be deprecated, as you cannot infer
which address or fqdn should be used.

Change-Id: I956bd7db7e55245081139d12d5c649194162894f
Addresses-Issue: Jira/AQUILON-2803, Jira/DHCP-46

guillaume-philippon/aquilon,guillaume-philippon/aquilon,quattor/aquilon,quattor/aquilon,quattor/aquilon,guillaume-philippon/aquilon