fixing the private DNS zone issue.

Private hosted zones will never be visible to third-parties like LetsEncrypt, and Lemur should not consider them as authoritative zones.
This fix, make sure  they are not added to the  dns_provider table.

lemur/plugins/lemur_acme/route53.py

@@ -35,6 +35,7 @@ def get_zones(client=None):
     zones = []
     for page in paginator.paginate():
         for zone in page["HostedZones"]:
+            if not zone["Config"]["PrivateZone"]:
                 zones.append(
                     zone["Name"][:-1]
                 )  # We need [:-1] to strip out the trailing dot.