docker container fails to start after stopping

I submitted a pull request on github, but it appears that you prefer
to use a mailing list for such things.

Attached is a patch to correct the behavior in the Docker container.

The problem is that apache generates httpd.pid at startup and it is
never removed.  When the container is stopped, the file remains.  At
startup httpd fails to start because it believes that httpd is already
running.

The patch simply deletes this file before starting httpd.

-M