performancecontrol: fix for NPE on boot

There is no need to cast the Context to an Activity which
will fail if it is called from BootService

   1: E/AndroidRuntime( 2773): FATAL EXCEPTION: AsyncTask #1
   2: E/AndroidRuntime( 2773): java.lang.RuntimeException: An error occured while executing doInBackground()
   3: E/AndroidRuntime( 2773): at android.os.AsyncTask.done(AsyncTask.java:299)
   4: E/AndroidRuntime( 2773): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
   5: E/AndroidRuntime( 2773): at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
   6: E/AndroidRuntime( 2773): at java.util.concurrent.FutureTask.run(FutureTask.java:239)
   7: E/AndroidRuntime( 2773): at android.os.AsyncTask.run(AsyncTask.java:230)
   8: E/AndroidRuntime( 2773): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
   9: E/AndroidRuntime( 2773): at java.util.concurrent.ThreadPoolExecutor.run(ThreadPoolExecutor.java:573)
  10: E/AndroidRuntime( 2773): at java.lang.Thread.run(Thread.java:841)
  11: E/AndroidRuntime( 2773): Caused by: java.lang.ClassCastException: com.brewcrewfoo.performance.service.BootService cannot be cast to android.app.Activity
  12: E/AndroidRuntime( 2773): at com.brewcrewfoo.performance.util.Helpers.shExec(Helpers.java:427)
  13: E/AndroidRuntime( 2773): at com.brewcrewfoo.performance.service.BootService.doInBackground(BootService.java:289)
  14: E/AndroidRuntime( 2773): at com.brewcrewfoo.performance.service.BootService.doInBackground(BootService.java:61)
  15: E/AndroidRuntime( 2773): at android.os.AsyncTask.call(AsyncTask.java:287)
  16: E/AndroidRuntime( 2773): at java.util.concurrent.FutureTask.run(FutureTask.java:234)

Change-Id: I93fa6f0287d1319d1074b53261be7c9783badcc1
Merge "performancecontrol: fix for NPE on boot" into jb-mr2