fs_mgr: system_other does not want overlayfs.

system wants overlayfs, and system_other is a valid candidate;
but system_other does not want overlayfs.

Addresses these denials:
avc: denied { read write } for comm="tune2fs" name="sda6" dev="tmpfs" ino=15114
  scontext=u:r:fsck:s0 tcontext=u:object_r:system_block_device:s0 tclass=blk_file permissive=0
avc: denied { read } for comm="e2fsck" name="sda6" dev="tmpfs" ino=15114
  scontext=u:r:fsck:s0 tcontext=u:object_r:system_block_device:s0 tclass=blk_file permissive=0
avc: denied { read write } for comm="e2fsck" name="sda6" dev="tmpfs" ino=15114
  scontext=u:r:fsck:s0 tcontext=u:object_r:system_block_device:s0 tclass=blk_file permissive=0

Fixes: 122454600
Test: boot, no tune2fs and e2fsck denials

Change-Id: Icce20f1463cfde034a56f25590cba9f8fe5f41a4