add support for fsck.f2fs

The Nexus 9 uses f2fs for /data. Make sure to properly label
/system/bin/fsck.f2fs so that the appropriate domain transition occurs.
Add support for getattr on devpts, required for fsck.f2fs.

Addresses the following denials:

  avc:  denied  { execute_no_trans } for  pid=172 comm="init" path="/system/bin/fsck.f2fs" dev="dm-0" ino=272 scontext=u:r:init:s0 tcontext=u:object_r:system_file:s0 tclass=file permissive=0
  avc:  denied  { getattr } for  pid=170 comm="fsck.f2fs" path="/dev/pts/0" dev="devpts" ino=3 scontext=u:r:fsck:s0 tcontext=u:object_r:devpts:s0 tclass=chr_file permissive=1

Change-Id: I34b3f91374d1eb3fb4ba76abce14ff67db259f96