simpleperf: fix scripts.

1. NDK may appear in either <sdk_path>/ndk/<ndk_version> or
<sdk_path>/ndk-bundle (the old way). So refactor find_tool_path() in
utils.py to support both.
2. Run inferno.py as a script instead of module, otherwise it doesn't
work in python3.
3. Use AdbHelper in test_monitor.py.

Bug: 169090018
Test: run test_monitor.py on linux/darwin/windows.
Change-Id: Ie7e65436a00022195bac3b657b4b0401e9e4548c
4 files changed