Create sysfs_hwrandom type.

HwRngTest needs access to the hwrandom sysfs files, but untrused_app
does not have access to sysfs.  Give these files their own label and
allow the needed read access.

(cherry-pick from internal commit: 85c0f8affa4d3aa3c50331e272327e360eb8bed9)

Bug: 27263241
Change-Id: If572ad0931a534d76e148b688b76687460e99af9
diff --git a/file_contexts b/file_contexts
index c06fcbd..785dc9e 100644
--- a/file_contexts
+++ b/file_contexts
@@ -327,6 +327,7 @@
 /sys/devices/system/cpu(/.*)?    u:object_r:sysfs_devices_system_cpu:s0
 /sys/devices/virtual/block/zram\d+(/.*)?     u:object_r:sysfs_zram:s0
 /sys/devices/virtual/block/zram\d+/uevent    u:object_r:sysfs_zram_uevent:s0
+/sys/devices/virtual/misc/hw_random(/.*)?    u:object_r:sysfs_hwrandom:s0
 /sys/power/wake_lock -- u:object_r:sysfs_wake_lock:s0
 /sys/power/wake_unlock -- u:object_r:sysfs_wake_lock:s0
 /sys/kernel/uevent_helper --	u:object_r:usermodehelper:s0