linux: Install EPEL repo

manifests/profiles/linux.pp

@@ -28,6 +28,8 @@ class icinga2_testing::profiles::linux
     }
   }
   elsif $::osfamily == 'RedHat' {
+    ensure_packages(['epel-release'])
+
     yumrepo { 'puppetlabs-products':
       descr   => 'Puppetlabs 3.x products repository - RHEL $releasever $basearch',
       baseurl => 'https://yum.puppetlabs.com/el/$releasever/products/$basearch',