Update 00-mpm.conf.jinja

Change mpm.conf template for RedHat family systems.

The code currently written will always expand to true as a pillar.get() call will return None in case the pillar is non existing, which is also considered defined.
Fix this.

apache/files/RedHat/conf.modules.d/00-mpm.conf.jinja

@@ -4,7 +4,7 @@
 
 {% set mpm_module = 'mpm_prefork' -%}
 {% set mpm_param = salt['pillar.get']('apache:mod_mpm_prefork', {}) -%}
-{% if pillar.get('apache:mod_mpm_worker') is defined -%}
+{% if pillar.get('apache:mod_mpm_worker', None) -%}
 {% set mpm_module = 'mpm_worker' -%}
 {% set mpm_param = salt['pillar.get']('apache:mod_mpm_worker', {}) -%}
 {% else -%}