Add host_environment to NamedServiceInstance
Add host_environment to NamedServiceInstance

The new field is needed to represent environment overrides for required
services.

Change-Id: I6d782550441d6b3b15cfb901d590d511efce4706
Reviewed-by: Dave Reeve <6a84ee3ae0690d4584b99406fb3076392171f50e@morganstanley.com>

quattor/aquilon-protocols,quattor/aquilon-protocols