Use a mock for OCSP responder test.
Use a mock for OCSP responder test.

This reduces the use of a "real" SA in our tests, which will eventually allow us
to run them in parallel.
letsencrypt/boulder,jcjones/boulder,jfrazelle/boulder,benileo/boulder,jsha/boulder,ibukanov/boulder,lucasallan/boulder,ZCloud-Firstserver/boulder,ZCloud-Firstserver/boulder,letsencrypt/boulder,jfrazelle/boulder,letsencrypt/boulder,bmw/boulder,patf/boulder,bmw/boulder,patf/boulder,jfrazelle/boulder,ibukanov/boulder,ZCloud-Firstserver/boulder,ZCloud-Firstserver/boulder,benileo/boulder,lucasallan/boulder,benileo/boulder,jcjones/boulder,jcjones/boulder,jfrazelle/boulder,sophie-h/boulder,sophie-h/boulder,lucasallan/boulder,benileo/boulder,jsha/boulder,ibukanov/boulder,jsha/boulder,sophie-h/boulder,bmw/boulder,jcjones/boulder,patf/boulder,patf/boulder