refine recovery domain.

Make sure we have all necessary rules to modify system_file and
exec_type.

Allow writing to /proc/sys/vm/drop_caches and other proc
files.

Addresses denials like:

  avc:  denied  { getattr } for  pid=152 comm="update_binary" path="/system/bin/debuggerd" dev="mmcblk0p21" ino=88 scontext=u:r:recovery:s0 tcontext=u:object_r:debuggerd_exec:s0 tclass=file
  avc:  denied  { read } for  pid=152 comm="update_binary" name="debuggerd" dev="mmcblk0p21" ino=88 scontext=u:r:recovery:s0 tcontext=u:object_r:debuggerd_exec:s0 tclass=file
  avc:  denied  { open } for  pid=152 comm="update_binary" name="debuggerd" dev="mmcblk0p21" ino=88 scontext=u:r:recovery:s0 tcontext=u:object_r:debuggerd_exec:s0 tclass=file
  avc:  denied  { remove_name } for  pid=152 comm="update_binary" name="framework.jar" dev="mmcblk0p21" ino=1600 scontext=u:r:recovery:s0 tcontext=u:object_r:system_file:s0 tclass=dir
  avc:  denied  { add_name } for  pid=152 comm="update_binary" name="Foo.apk.patch" scontext=u:r:recovery:s0 tcontext=u:object_r:system_file:s0 tclass=dir
  avc:  denied  { write } for  pid=152 comm="update_binary" name="drop_caches" dev="proc" ino=8288 scontext=u:r:recovery:s0 tcontext=u:object_r:proc:s0 tclass=file

recovery is still in permissive_or_unconfined(), so no rules are
being enforced.

Change-Id: I14ca777fe27a2b0fd9a0aefce5ddcc402b1e5a59