Break up the device-mapper trainwreck

Break the device-mapper plug-in up into separate plugins for dm
itself and each of the current device-mapper applications:

 - devicemapper.py
 - dmraid.py
 - block.py
 - lvm2.py
 - md.py

The data collection for each subsystem is largely unchanged other
than to fix bugs and remove obsolete items:

 - support for multipath bindings in /var dropped
   (only relevant to RHEL5 and earlier)
 - collect multipath -l separately from -ll
 - fix 'udevinfo' -> 'udevadm info'

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>