LU-3352 test: use correct nettype in conf-sanity.sh test_73

Use $NETTYPE instead of tcp to set failnode NID in conf-sanity.sh
test_73.

Test-Parameters: nettypes=o2ib testlist=conf-sanity
Signed-off-by: Liu Ying <emoly.liu@intel.com>
Change-Id: Ibcc1e60c2369aafada28e7d7462cb7dbb1ce5043
Reviewed-on: http://review.whamcloud.com/6550
Tested-by: Hudson
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>