dm mpath: hp retry if not ready

This patch adds retries to the hp hardware handler, and utilizes the
MP_RETRY flag of dm-multipath.  For now in the hp handler, if we get a
pg_init completed with a check condition we just assume we can retry the
pg_init command.  We make this assumption because of incomplete data on
specific check condition code of the HP hardware, and because testing
has shown the HP path initialization command to be idempotent.
The number of times we retry is settable via the "pg_init_retries"
multipath map feature.

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Acked-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>