Incremental: improve support for "DEVICE" based restriction in mdadm.conf

Incremental: improve support for "DEVICE" based restriction in mdadm.conf

--incremental currently fails if the device name passed does not
textually match the names permitted by the DEVICE line in mdadm.conf.
This is problematic when "mdadm -I" is run by udev as the name given
can be a temp name.

This patch makes two improvements:
1/ We generate a list of all existing devices that match the names
  in mdadm.conf, and allow rdev based matching
2/ We allows extra aliases to be provided on the command line, and
  perform textual matching on those.  This is particularly suitable
  for udev usages as ${DEVLINKS} can be provided even though the links
  make not yet be created.

Signed-off-by: NeilBrown <neilb@suse.de>