Ensure we're using mpm_event, not mpm_prefork.

We'll end up with prefork if we use mod_php, so... don't.

states/apache/init.sls

@@ -25,6 +25,12 @@ apache_include_module:
   apache_module.enabled:
     - name: include
 
+apache_mpm_module:
+  apache_module.disabled:
+    - name: mpm_prefork
+  apache_module.enabled:
+    - name: mpm_event
+
 apache_proxy_module:
   apache_module.enabled:
     - name: proxy