Switch Centos/Fedora to Apache woker MPM

In trying to debug periodic gate instability of CentOS, I noticed that
it is using the prefork mpm, while Ubuntu is defaulting to the
multi-threaded worker mpm.

One of the problems seems related to 502 proxy errors from the TLS
proxy.  We see out-of-sync timestamps in the centos TLS proxy access
logs, which might be innocent behaviour based on the prefork model or
indicate something else.

Before going too deep down this rabbit-hole, I think it is better for
consistency to use the same mpm model on all our platforms, and start
debugging from there.

Change-Id: I9881f2e7d51fdd9fc0f7fb3e37179aa53171b531

Author: ianw

lib/apache

@@ -132,6 +132,10 @@ function install_apache_wsgi {
     elif is_fedora; then
         sudo rm -f /etc/httpd/conf.d/000-*
         install_package httpd mod_wsgi
+        # For consistency with Ubuntu, switch to the worker mpm, as
+        # the default is prefork
+        sudo sed -i '/mod_mpm_prefork.so/s/^/#/g' /etc/httpd/conf.modules.d/00-mpm.conf
+        sudo sed -i '/mod_mpm_worker.so/s/^#//g' /etc/httpd/conf.modules.d/00-mpm.conf
     elif is_suse; then
         install_package apache2 apache2-mod_wsgi
     else