[contrib] validate_failures.py: Renaming cleanup

Rename _VALID_TEST_RESULTS* to _INTERESTING_RESULTS*,
which better describes the purpose.  Subsequent patch
will define _VALID_TEST_RESULTS to accept all valid
result entries, including PASS, XFAIL, etc.

Change-Id: Iad74d058d48f40ba08d9a87e18f93770fd6e4089
1 file changed