Change the semantics of stop_master RPC

To avoid polluting the stop_master RPC interface with network
parameters, this patch removes the deactivation of the master IP from
this RPC.

The call to deactivate_master_ip is then added before every stop_master
call.

Signed-off-by: Andrea Spadaccini <spadaccio@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>