LU-5092 nodemap: remove nodemap_idx_action, only act on MGS

LU-5092 nodemap: remove nodemap_idx_action, only act on MGS

Only the MGS config needs to be modified on config changes.
The target configs will be loaded from the MGS and written
whole to disk.

Signed-off-by: Kit Westneat <kit.westneat@gmail.com>
Change-Id: I3114258d6e18d293cdf29ae47a28465f245387de
Reviewed-on: http://review.whamcloud.com/18554
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>