simpleperf: prepare for merging test_monitor.py.

1. Refactor TestHelper class to remove global variable and add explicit
init class method.
2. Merge TestLogger into TestHelper.
3. Move build_testdata() into do_test.py.
4. Move test filter into an explicit function.

Bug: 182507493
Test: run test.py.
Change-Id: Ia76baa17197f6134ec4d7868e764edb66d29b6bd
15 files changed