Label ranchu block devices.

Address the following denials:
avc:  denied  { getattr } for  pid=1166 comm="e2fsck" path="/dev/block/vdc" dev="tmpfs" ino=2880 scontext=u:r:fsck:s0 tcontext=u:object_r:block_device:s0 tclass=blk_file permissive=0
avc:  denied  { read write } for  pid=1166 comm="e2fsck" name="vdc" dev="tmpfs" ino=2880 scontext=u:r:fsck:s0 tcontext=u:object_r:block_device:s0 tclass=blk_file permissive=0

Bug: 27224003
Change-Id: I4792420822d238e6ad1bf757634c924b95150515
diff --git a/target/board/generic/sepolicy/file_contexts b/target/board/generic/sepolicy/file_contexts
index e704a8e..e8d32f7 100644
--- a/target/board/generic/sepolicy/file_contexts
+++ b/target/board/generic/sepolicy/file_contexts
@@ -1,6 +1,13 @@
+# goldfish
 /dev/block/mtdblock0         u:object_r:system_block_device:s0
 /dev/block/mtdblock1         u:object_r:userdata_block_device:s0
 /dev/block/mtdblock2         u:object_r:cache_block_device:s0
+
+# ranchu
+/dev/block/vda               u:object_r:system_block_device:s0
+/dev/block/vdb               u:object_r:cache_block_device:s0
+/dev/block/vdc               u:object_r:userdata_block_device:s0
+
 /dev/goldfish_pipe           u:object_r:qemu_device:s0
 /dev/qemu_.*                 u:object_r:qemu_device:s0
 /dev/socket/qemud            u:object_r:qemud_socket:s0