Label all files under /sys/qemu_trace with sysfs_writable.

Otherwise we have different security contexts but the same DAC
permissions:
-rw-rw-rw- root     root              u:object_r:sysfs_writable:s0 process_name
-rw-rw-rw- root     root              u:object_r:sysfs:s0 state
-rw-rw-rw- root     root              u:object_r:sysfs:s0 symbol

This change fixes denials such as:
type=1400 msg=audit(1379096020.770:144): avc:  denied  { write } for  pid=85 comm="SurfaceFlinger" name="symbol" dev="sysfs" ino=47 scontext=u:r:surfaceflinger:s0 tcontext=u:object_r:sysfs:s0 tclass=file

Change-Id: I261c7751da3778ee9241ec6b5476e8d9f96ba5ed
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

file_contexts

@@ -208,7 +208,7 @@
 #############################
 # sysfs files
 #
-/sys/qemu_trace/process_name	--	u:object_r:sysfs_writable:s0
+/sys/qemu_trace(/.*)?	--	u:object_r:sysfs_writable:s0
 /sys/devices/platform/nfc-power/nfc_power -- u:object_r:sysfs_nfc_power_writable:s0
 /sys/class/rfkill/rfkill[0-9]*/state -- u:object_r:sysfs_bluetooth_writable:s0
 /sys/class/rfkill/rfkill[0-9]*/type -- u:object_r:sysfs_bluetooth_writable:s0