Adding test for reader compatibility

Reader + Parser v3 should be able to read V2 cow format written to disk.
This test reads in a small cow file written by basic_v2_cow_writer and
parses it to ensure this compatibility checks out.

Test: cow_api_test
Change-Id: I46ebf4e3f12cdb3e4716ca5b624aab5836086733
2 files changed