Allow init to write to userdata/cache

Init will format userdata and cache partitions if asked.

Addresses denials such as:
type=1400 audit(55.329:5): avc:  denied  { write } for  pid=228 comm="init" name="mmcblk0p38" dev="tmpfs" ino=8911 scontext=u:r:init:s0 tcontext=u:object_r:cache_block_device:s0 tclass=blk_file permissive=0

Bug: 22531242
Change-Id: If4863f4c06e05a36cfccdd9aba321eb1f479dddd
1 file changed