LU-2608 tests: check_catastrophe success on failure to connect

Allow check_catastrophe to pass on failure to connect to host.
Otherwise LBUG assertions crop up when hosts are overloaded.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Ie873b817911613369a226341d8efe06707b08bc4
Reviewed-on: http://review.whamcloud.com/5200
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>