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.

Bug: 27263241
Change-Id: I718ba485e9e6627bac6e579f746658d85134b24b
diff --git a/file_contexts b/file_contexts
index a3cebbf..5739556 100644
--- a/file_contexts
+++ b/file_contexts
@@ -356,6 +356,7 @@
 /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