puppet: Stop automatically creating hiera.yaml on newer distros.

This fixes some unnecessary warnings on systems running Ubuntu bionic.

scripts/zulip-puppet-apply

@@ -17,8 +17,10 @@ config = configparser.RawConfigParser()
 config.read("/etc/zulip/zulip.conf")
 
 if not os.path.exists("/etc/puppet/hiera.yaml"):
-    # Suppress warnings about hiera.yaml not existing.
-    subprocess.check_call(["touch", "/etc/puppet/hiera.yaml"])
+    codename = subprocess.check_output(["lsb_release", "-cs"]).strip().decode("utf-8")
+    if codename in ["trusty", "stretch", "xenial"]:
+        # Suppress warnings in old puppet about hiera.yaml not existing.
+        subprocess.check_call(["touch", "/etc/puppet/hiera.yaml"])
 
 puppet_config = """
 Exec { path => "/usr/sbin:/usr/bin:/sbin:/bin" }