Fix watherclient error in py3

watchercliet will raise error:
Recoverable error: sequence item 0: expected str instance, bytes found

This patch fix this.

Change-Id: I6fe21766f320b0a09a14202203a5d0451175e1d3

watcherclient/common/httpclient.py

@@ -354,7 +354,15 @@ class HTTPClient(VersionNegotiationMixin):
         # Read body into string if it isn't obviously image data
         body_str = None
         if resp.headers.get('Content-Type') != 'application/octet-stream':
-            body_str = ''.join([chunk for chunk in body_iter])
+            # decoding byte to string is necessary for Python 3 compatibility
+            # this issues has not been found with Python 3 unit tests
+            # because the test creates a fake http response of type str
+            # the if statement satisfies test (str) and real (bytes) behavior
+            body_list = [
+                chunk.decode("utf-8") if isinstance(chunk, bytes)
+                else chunk for chunk in body_iter
+            ]
+            body_str = ''.join(body_list)
             self.log_http_response(resp, body_str)
             body_iter = six.StringIO(body_str)
         else: