simpleperf: fix runtest.

1. Adjust function_fork.cpp and two_functions.cpp to make functions
not combined by compiler.
2. Download simpleperf and runtest executables on device before
testing on device.
3. Find config file in the same directory as runtest.py instead of
relying that it is in current directory.

Bug: http://b/30413567
Change-Id: I4ed9964f443c8cc75f4cb352ff1f13fb11104c89
Test: mmma system/extras/simpleperf && python system/extras/simpleperf/runtest/runtest.py
3 files changed