Add a --with-test-suite option for "in-tree" testing

Step one. It's not actually "in-tree" yet, since it requires running
`make install` first, but at least it gives us a `make check`.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/trunk-test-integration@1777384 13f79535-47bb-0310-9956-ffa450edef68