LU-14773 tests: skip check_network() on working node

LU-14773 tests: skip check_network() on working node

Don't call check_network() (which can take several seconds per node)
if the get_param command ran successfully on all of the nodes.  The
get_param success implies the connection to the remote nodes works
properly, and completes more quickly.

For consistency with previous behavior, still call check_network() if
get_param didn't return any output, since the modules may be unloaded.

Remove some extra visual clutter from every subtest.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I6a11cf8a1a6b43bebc3ff8f5506e1faac13ebbe5
Reviewed-on: https://review.whamcloud.com/44033
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Elena Gryaznova <elena.gryaznova@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>