multipath: add detect_prio option to autodetect

multipath: add detect_prio option to autodetect

This patch adds a new multipath.conf option, detect_prio.  If set to yes,
multipathd will try to determine the correct prioritizer for the device. If
it finds one, that will be used instead of its configured prioritizer.  If
none is found, the configured prioritizer will be used.  It can currently
only detect ALUA devices.

Also fixed and issue with select_prio where in the devices section, it was
passing in the prio name string instead of the prio args string to prio_get()

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>