puppet: Detect CentOS for release_name.

puppet/zulip/manifests/base.pp

@@ -20,6 +20,8 @@ class zulip::base {
   ]
   package { $base_packages: ensure => 'installed' }
 
+  case $::osfamily {
+    'debian': {
       $release_name = $::operatingsystemrelease ? {
         # Debian releases
         /^7.[0-9]*/ => 'wheezy',
@@ -33,6 +35,11 @@ class zulip::base {
         '16.04' => 'xenial',
         '18.04' => 'bionic',
       }
+    }
+    'redhat': {
+      $release_name = "${::operatingsystem}${::operatingsystemmajrelease}"
+    }
+  }
 
   $postgres_version = $release_name ? {
     'wheezy'  => '9.1',
@@ -44,6 +51,7 @@ class zulip::base {
     'wily'    => '9.4',
     'xenial'  => '9.5',
     'bionic'  => '10',
+    'CentOS7' => '10',
   }
 
   $normal_queues = [