dm mpath: skip activate_path for failed paths

This patch adds two minor fixes while processing device mapper path activation.

Skip failed paths while calling activate_path.  If the path is already failed
then activate_path will fail for sure. We don't have to call in that case. In
some case this might cause prolonged retries unnecessarily.

Change the misleading message if the path being activated fails with SCSI_DH_NOSYS.

Signed-off-by: Babu Moger <babu.moger@lsi.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>