parse traces from ext4 events
Created by: kdub
Adds trace parsing for ext4_da_write_begin, ext4_da_write_end, ext4_sync_file_enter, and ext4_sync_file_exit events
Test: run the 4 new unit tests (nosetests tests/test_filesystem.py) Change-Id: I9b7049d5e9879cc3dedb5fd9d3d1433fa8304618