su.te: add filesystem dontaudit rule

Addresses su denials which occur when mounting filesystems not
defined by policy.

Addresses denials similar to:

  avc: denied { mount } for pid=12361 comm="mount" name="/" dev="binfmt_misc" ino=1 scontext=u:r:su:s0 tcontext=u:object_r:unlabeled:s0 tclass=filesystem permissive=1

Change-Id: Ifa0d7c781152f9ebdda9534ac3a04da151f8d78e