fix persistent process is killed and restart again and again

start presistent app  before system booting, in NewProcessRecordLocked
will set  persistent = true, but not set r.maxAdj = ProcessList.PERSISTENT_PROC_ADJ.
so this process  may become CACHED_EMPTY, then be killed.
while persistent = true, will restart again.

https://code.google.com/p/android/issues/detail?id=222224

Change-Id: I91b405ca3f3bbe8934e4a495d9a54eab4f51e21f