REGTEST: set retries count to zero for all tests that expect at 503

REGTEST: set retries count to zero for all tests that expect at 503

Some tests expect a 503, typically those that check that wrong CA/CRL
will not be accepted between a server and a frontend. But such tests
tend to last very long simply because of the 1-second turn-around on
connection retries that happens during the failure. Let's properly set
the retries count to zero for these ones. One test purposely wants to
exhaust the retries so the retries was set to 1 instead.