Use mod_cgid and multithreading instead of mod_cgi

The default configuration used preforking for multi processing.
This requires to use mod_cgi for executing CGI scripts. However,
git-http-backend allows to use threading for multi processing.
This then seems to be the better solution and can be done by
using mod_mpm_event instead of mod_mpm_prefork [1]. For
executing CGI scripts in a multi-threaded environment the
mod_cgid has to be used.

[1] https://serverfault.com/questions/383526/how-do-i-select-which-apache-mpm-to-use/383634#383634

Change-Id: Iff366444a2dcccc53c1334bb4beb625e81a97781
diff --git a/container-images/apache-git-http-backend/config/httpd.conf b/container-images/apache-git-http-backend/config/httpd.conf
index d91ef8d..7a28460 100644
--- a/container-images/apache-git-http-backend/config/httpd.conf
+++ b/container-images/apache-git-http-backend/config/httpd.conf
@@ -72,8 +72,8 @@
 # Example:
 # LoadModule foo_module modules/mod_foo.so
 #
-#LoadModule mpm_event_module modules/mod_mpm_event.so
-LoadModule mpm_prefork_module modules/mod_mpm_prefork.so
+LoadModule mpm_event_module modules/mod_mpm_event.so
+#LoadModule mpm_prefork_module modules/mod_mpm_prefork.so
 #LoadModule mpm_worker_module modules/mod_mpm_worker.so
 LoadModule authn_file_module modules/mod_authn_file.so
 #LoadModule authn_dbm_module modules/mod_authn_dbm.so