Support using a common redis connection

If sentinel_host or sentinel_cluster_id is not provided it will try to
connect with a redis_host parameter

server/extension/sql/0.5.0/85_isodistance.sql

@@ -0,0 +1,18 @@
+CREATE OR REPLACE FUNCTION cdb_dataservices_server.cdb_isodistance(username TEXT, orgname TEXT, source geometry(Geometry, 4326), mode TEXT, range integer[], options text[] DEFAULT array[]::text[])
+RETURNS SETOF cdb_dataservices_server.isoline AS $$
+  plpy.execute("SELECT cdb_dataservices_server._connect_to_redis('{0}')".format(username))
+  redis_conn = GD["redis_connection_{0}".format(username)]['redis_metrics_connection']
+  plpy.execute("SELECT cdb_dataservices_server._get_routing_config({0}, {1})".format(plpy.quote_nullable(username), plpy.quote_nullable(orgname)))
+  user_isolines_config = GD["user_routing_config_{0}".format(username)]
+  type = 'isodistance'
+
+  here_plan = plpy.prepare("SELECT cdb_dataservices_server._cdb_here_routing_isolines($1, $2, $3, $4, $5, $6, $7) as isoline; ", ["text", "text", "text", "geometry(Geometry, 4326)", "text", "integer[]", "text[]"])
+  result = plpy.execute(here_plan, [username, orgname, type, source, mode, range, options])
+  isolines = []
+  for element in result:
+    isoline = element['isoline']
+    isoline = isoline.translate(None, "()").split(',')
+    isolines.append(isoline)
+
+  return isolines
+$$ LANGUAGE plpythonu;