Remove chown of /mnt directory

/mnt is always owned by root in vanilla images,
so we don't need to do chown.

Also execution "chown root:root /mnt" may be run
after plugin command "chown -R hadoop:hadoop /mnt"
sometimes (if plugin will make chown before rc.local script)
and then datanode can't be started.

Change-Id: If72308a9969fd9d1bf8bab58f8294b43fb292957
Partial-bug: #1324582
Closes-bug: #1295807
Merge "Remove chown of /mnt directory"