allow shell self:process ptrace;

Allow the non-privileged adb shell user to run strace. Without
this patch, the command "strace /system/bin/ls" fails with the
following error:

  shell@android:/ $ strace /system/bin/ls
  strace: ptrace(PTRACE_TRACEME, ...): Permission denied
  +++ exited with 1 +++

Change-Id: I207fe0f71941bff55dbeb6fe130e636418f333ee