Add atrace_userdebug.rc to enable some tracepoints for userdebug only.

These tracepoints are currently approved by security for userdebug only
(see linked bug).

These are enabled for use in Traceur, which is currently only available
for userdebug builds.

Bug: 37110010
Test: Compiled and installed for userdebug and verified correct permissions
for a file in atrace.rc as well as a file in atrace_userdebug.rc:

(atrace_userdebug.rc)
$ adb shell ls -al /sys/kernel/debug/tracing/events/workqueue/enable
-rw-rw-rw- 1 root shell 0 1970-01-01 00:00 /sys/kernel/debug/tracing/events/workqueue/enable

(atrace.rc only)
$ adb shell ls -al /sys/kernel/debug/tracing/trace_clock
-rw-rw-r-- 1 root shell 0 1970-01-01 00:00 /sys/kernel/debug/tracing/trace_clock

Test: Compiled and installed a user build and verified correct
permissions for the file modified in atrace.rc, but that
atrace_userdebug.rc was not executed:

(atrace_userdebug.rc)
$ adb shell ls -al
/sys/kernel/debug/tracing/events/workqueue/enable
-rw-r--r-- 1 root root 0 1969-12-31 19:00

(atrace.rc
$ adb shell ls -al /sys/kernel/debug/tracing/trace_clock
-rw-rw-r-- 1 root shell 0 1969-12-31 19:00
/sys/kernel/debug/tracing/trace_clock

Change-Id: Ifb0ce9942a2e7a48f480b46bf944fcbc69c1707d