LU-3375 test: use available mdc for replay-single test_44

LU-3375 test: use available mdc for replay-single test_44

This patch corrects that to only look for the available mdc device
whose status is "UP".

Test-Parameters: clientdistro=fc18 clientarch=x86_64 serverdistro=el6 serverarch=x86_64 testlist=replay-single envdefinitions=SLOW=yes
Signed-off-by: Liu Ying <emoly.liu@intel.com>
Change-Id: Ia4013e68f44b0c1c5eb173b04af4c8c67e4961cf
Reviewed-on: http://review.whamcloud.com/6425
Tested-by: Hudson
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>