Deprecate conductor ping method.

Deprecate the ping() method of the conductor API in favor of the one
that comes with the base rpc API.

Part of blueprint base-rpc-api.

Change-Id: Iea46b7f6ce70f4919d0121433af2fd64d6346941
Move get_backdoor_port to base rpc API.

Each service implemented the get_backdoor_port method individually.  This
patch moves the implementation of this method to the base rpc API
instead, and removes the now unnecessary code from each of the services.
The server side method was left on all of the managers for rpc backwards
copmatibility.  They can be removed on the next major rpc version bump
of those APIs.

Part of blueprint base-rpc-api.

Change-Id: Ia8838fafd80eb86a1c2d66f5e97370042d8d8c53
Merge "Deprecate conductor ping method."
Merge "Move get_backdoor_port to base rpc API."