Service Registration using conf file

Making the DB specific settings for Service
Registry configuration driven that will help
in addition/removal/modification dynamically
for new service type.

Format for adding new service type in guestagen
config file will be -
service_registry_ext  = <add service type in dictonary>

implements: blueprint configuration-driven-changes

Change-Id: I0fc1a80f0fa70dbc0c477e31b5374d156bb03488
Merge "Service Registration using conf file"