Merge /httpd/httpd/trunk:r1923148

Merge /httpd/httpd/trunk:r1923148

  *) mod_md: update to version 2.4.31
     - Improved error reporting when waiting for ACME server to verify domains
       or finalizing the order fails, e.g. times out.
     - Increasing the timeouts to wait for ACME server to verify domain names
       and issue the certificate from 30 seconds to 5 minutes.
     - Change a log level from error to debug when Stapling is enabled but a
       certificate carries no OCSP responder URL.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1923150 13f79535-47bb-0310-9956-ffa450edef68