Zygote: Add CAP_WAKE_ALARM to system_server to properly support timerfd alarms

The when the timerfd alarm logic was added to the kernel, an oversight was made
and the interface does not check for the CAP_WAKE_ALARM permissions as required
via other kernel methods to trigger an alarm timer.

In v4.8-rc kernels, the change 2895a5e5b3a ("timerfd: Reject ALARM timerfds
without CAP_WAKE_ALARM") was added by Eric Caruso <ejcaruso@google.com>.

After this change (which may be backported to -stable), the AlarmManager will
fail on the first timerfd_create call, and will not be able to set the time
or handle other necessary functions.

The solution here is to add CAP_WAKE_ALARM to the system_server process.

Change-Id: Ifdb16f3ef42711e553f727165de3922d484b5be4
Signed-off-by: John Stultz <john.stultz@linaro.org>