puppet: Add redis_password file for Nagios.

This allows the Nagios user to access redis without having full access
to the redis system.  Ideally, this would eventually use a password
that only has statistics read access, but I'm not sure redis supports
that.

puppet/zulip_ops/manifests/app_frontend.pp

@@ -62,4 +62,13 @@ class zulip_ops::app_frontend {
     content => template("zulip_ops/supervisor/conf.d/redis_tunnel.conf.template.erb"),
     notify => Service["supervisor"],
   }
+  # Need redis_password in its own file for Nagios
+  file { '/var/lib/nagios/redis_password':
+    ensure     => file,
+    mode       => 600,
+    owner      => "nagios",
+    group      => "nagios",
+    content    => zulipsecret('secrets', 'redis_password', ''),
+  }
+
 }

puppet/zulip_ops/manifests/redis.pp

@@ -1,3 +1,13 @@
-class zulip_ops::redis inherits zulip::redis {
+class zulip_ops::redis {
   include zulip_ops::base
+  include zulip::redis
+
+  # Need redis_password in its own file for Nagios
+  file { '/var/lib/nagios/redis_password':
+    ensure     => file,
+    mode       => 600,
+    owner      => "nagios",
+    group      => "nagios",
+    content    => "${zulip::redis::redis_password}\n",
+  }
 }