Improve tests for HTTP validator. (#565)
Improve tests for HTTP validator. (#565)

* Make them table-driven tests so that we can test more edge cases and it's easier to see what's going on.
* Also test the behavior when specifying both the conditions -- status code and header.

PiperOrigin-RevId: 359071786
cloudprober/cloudprober,cloudprober/cloudprober,google/cloudprober,google/cloudprober,cloudprober/cloudprober