[CP-6333][CP-6334]: rm dm-multipath-dm-event, dm-multipath-disable-udev-rules

This patch is the counterpart of 2 patches removed in
dm-multipath (formerly dm-multipath in guest-packages.hg):
- dm-multipath-disable-udev-rules
- dm-multipath-dm-event

This patch basically does the following:
- ship and override multipath udev rules from sm RPM
- add rules to invoke mpathcount from udev

Note: for udev to catch the relevant events, the kernel must have
      DM_UEVENT enabled

Signed-off-by: Germano Percossi <germano.percossi@citrix.com>
Reviewed-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>

GitHub: closes #40 on xapi-project/sm