allow procrank to write to bug report

avc: denied { write } for pid=14742 comm="procrank" path="/data/data/com.android.shell/files/bugreports/bugreport-2015-07-02-22-17-43.txt.tmp" dev="dm-2" ino=44479 scontext=u:r:procrank:s0 tcontext=u:object_r:shell_data_file:s0 tclass=file permissive=0

Bug: 22400298
Change-Id: Ibf5dcf9f7edf416e977577afc32bbbef62e50974