mod_proxy_hcheck: take balancer's SSLProxy* directives into account.

trunk patch: http://svn.apache.org/r1836276
2.4.x patch: svn merge -c 1836276 ^/httpd/httpd/trunk .
+1: jim, ylavic, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1841261 13f79535-47bb-0310-9956-ffa450edef68