Only use default Jaeger endpoint when no endpoint is defined (census-instrumentation#325)

Author: achandras

opencensus/trace/exporters/jaeger_exporter.py

@@ -114,11 +114,10 @@ def collector(self):
         if self.host_name is None or self.port is None:
             return None
 
-        thrift_url = 'http://{}:{}{}{}'.format(
+        thrift_url = 'http://{}:{}{}'.format(
             self.host_name,
             self.port,
-            self.endpoint,
-            DEFAULT_ENDPOINT)
+            self.endpoint or DEFAULT_ENDPOINT)
 
         auth = None
         if self.username is not None and self.password is not None: