cpuset: Add allow_attach hook for cpusets on android.

cpuset: Add allow_attach hook for cpusets on android.

This patch provides a allow_attach hook for cpusets,
which resolves lots of the following logcat noise.

W SchedPolicy: add_tid_to_cgroup failed to write '2816' (Permission denied); fd=29
W ActivityManager: Failed setting process group of 2816 to 0
W System.err: java.lang.IllegalArgumentException
W System.err:    at android.os.Process.setProcessGroup(Native Method)
W System.err:    at com.android.server.am.ActivityManagerService.applyOomAdjLocked(ActivityManagerService.java:18763)
W System.err:    at com.android.server.am.ActivityManagerService.updateOomAdjLocked(ActivityManagerService.java:19028)
W System.err:    at com.android.server.am.ActivityManagerService.updateOomAdjLocked(ActivityManagerService.java:19106)
W System.err:    at com.android.server.am.ActiveServices.serviceDoneExecutingLocked(ActiveServices.java:2015)
W System.err:    at com.android.server.am.ActiveServices.publishServiceLocked(ActiveServices.java:905)
W System.err:    at com.android.server.am.ActivityManagerService.publishService(ActivityManagerService.java:16065)
W System.err:    at android.app.ActivityManagerNative.onTransact(ActivityManagerNative.java:1007)
W System.err:    at com.android.server.am.ActivityManagerService.onTransact(ActivityManagerService.java:2493)
W System.err:    at android.os.Binder.execTransact(Binder.java:453)

Change-Id: Ic1b61b2bbb7ce74c9e9422b5e22ee9078251de21
[Ported to 4.4, added commit message]
Signed-off-by: John Stultz <john.stultz@linaro.org>