Fix how header-checker tests run.

Previously, the tests mainly exercised header-abi-diff.
After this change, checked-in reference dumps are compared with
generated dumps. This allows us to:
  - get header-abi-dumper and header-abi-linker involved in testing
    better.
  - Know about any incompatbile message format changes made
    inadvertently.

Test: tests/test.py; all tests pass.

Change-Id: I7c7ba0811e6c08c6194a0a11616680279e7a0e1d
4 files changed