Med: Strip trailing slashes from device names in /proc/mounts

Entries for CIFS mounts can sometimes contain trailing slashes
in the device field in /proc/mounts.

For example:
$ mount
192.168.122.1/test on /mnt type cifs (rw)
$ grep test /proc/mounts
192.168.122.1/test/ /mnt cifs ...

This patch strips trailing slashes from device names when
reading the contents of /proc/mounts.

Resolves: rhbz#848642
Signed-off-by: Ryan McCabe <rmccabe@redhat.com>