Let apache module purge config

Otherwise can cause issues when enabling prefork as mpm_event is enabled
by default in httpd. A recent change in puppet-apache [1] has added
httpd.modules.conf directory to load, which includes default mpm config
that conflicts with prefork.

In the past we disabled purge because of issues with nagios [2], however
nagios deployment is not longer supported by packstack, so we can safely
enable apache config purge which is the default option.

[1] 6425cc46a8
[2] 686625e17b

Change-Id: Ifdccd8609658b3170b8356bddc5062f252677d40

packstack/puppet/modules/packstack/manifests/apache.pp

@@ -3,7 +3,6 @@ class packstack::apache ()
     # Use python3 for mod_wsg in fedora
     if ($::operatingsystem == 'Fedora') or ($::osfamily == 'RedHat' and Integer.new($::operatingsystemmajrelease) > 7)  {
       class { '::apache':
-        purge_configs => false,
         mod_packages  => merge($::apache::params::mod_packages, {
           'wsgi' => 'python3-mod_wsgi',
         }),
@@ -13,7 +12,6 @@ class packstack::apache ()
       }
     }else{
       class {'::apache':
-        purge_configs => false,
       }
     }