LU-15632 tests: Typo in check_node_health

LU-15632 tests: Typo in check_node_health

A typo in test-frameworks.sh::check_node_health() causes test failures
if "lctl get_param catastrophe" doesn't return any output.

Test-Parameters: trivial
Fixes: 67752f6db2 ("LU-14773 tests: skip check_network() on working node")
HPE-bug-id: LUS-10800
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: I5dbb46578a62f8fc13f39be6fbebe87c75bc2a7d
Reviewed-on: https://review.whamcloud.com/46746
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Elena Gryaznova <elena.gryaznova@hpe.com>