Remove instance_info_cache_update() from conductor

After network api was converted to use InfoCache object it no longer
depends on the conductor instance_info_cache_update() method.

This change removes this method from conductor and in addition removes
conductor parameter in calls to network api from within compute manager,
previously needed by the @refrech_cache() decorator in network api for
its calls to this same conductor method.

Change-Id: I5bb535062b5f5948e2b6ba1daa089f3d93471394