Add missing link for drivers resource

Add missing link for drivers resource to API V1 root controller
and update corresponding test.

Change-Id: I9ae0d6c0939b283b19a188955e67f7eaffeadeac
Closes-Bug: #1255952
Add heartbeat_interval to new 'conductor' cfg group

Add new 'conductor' config option group, to separate the various options
specific to this service which will be added in subsequent patches.

Add heartbeat_interval option to control how often a conductor updates
its status record in the database.

Fix a minor issue with the unit test associated with this method
and rename it to be more consistent with other unit test names.

Change-Id: I0ea71231ba7a6f20b94f4bca7de2a2f49bc4a428
Merge "Add missing link for drivers resource"