Add a pam module to set smack label (PTREL-549)

Add a pam module to set smack label (PTREL-549)

After some back and forth, this was deemed to be sufficient for now, as
other solutions where wrong in an equal number of cases, but where
substantially more complicated.

Adds a session module that just sets context to "User"

Change-Id: I5a72fee29519d89d6b8ea60cd970d0438a0cb7cd
Signed-off-by: Michael Leibowitz <michael.leibowitz@intel.com>