systemd: fix automount of media devices

JIRA: SB-4128

This will allow automount of media devices. If set in slave mode
there will be no more automount actions, even though the udevd
rules are read there will be no actual processing of mount/umount
actions.

Signed-off-by: Srikanth Krishnakar <Srikanth_Krishnakar@mentor.com>
Merge pull request #388 from skrishnakar/fix-udev-mount

systemd: fix automount of media devices