simpleperf: support profiling native programs in app_profiler.py.

simpleperf: support profiling native programs in app_profiler.py.

This is a preparation of using app_profiler.py in inferno.

In app_profiler.py:
Add -np option to profile native programs like surfaceflinger.
Add -cmd option to profile command lines.
Add --arch option to set the app arch, because we don't guess the app arch
when profiling command lines.
Add corresponding tests in test.py.

Also improve the way of detecting whether the device supports trace-offcpu.

Bug: http://b/63006886
Test: run test.py.

Change-Id: Id899063d9a94beec67b22fd7710cda7a438557fb