Enable zero-install testing

By pointing a local apxs script and corresponding config file into the
build tree, we can trick Apache::Test into testing a server that hasn't
actually been installed.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/trunk-test-integration@1777667 13f79535-47bb-0310-9956-ffa450edef68