Merge r417443 from trunk:

* Retry worker chosen by client supplied route / redirect worker if it
  is in error state before sending "Service Temporarily Unavailable".

PR: 38962
Submitted by: Christian Boitel <cboitel lfdj.com>
Reviewed by: rpluem

Submitted by: rpluem
Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@437745 13f79535-47bb-0310-9956-ffa450edef68