Fix Non-OpenStack dynamic pollster credentials handling

There was a problem with the barbican credentials processing for
Non-OpenStack dynamic pollster. The credentials variables would be
retrieved as a byte string, which would break the processing.
Therefore, we needed to introduce a method to check if the credentials
are a String object. if they are not, we convert them to String.

Change-Id: I2084061eb8f543d4c557963599732e35cfa22996

ceilometer/polling/dynamic_pollster.py

@@ -850,6 +850,9 @@ class NonOpenStackApisSamplesGatherer(PollsterSampleGatherer):
         if override_credentials:
             credentials = override_credentials
 
+        if not isinstance(credentials, str):
+            credentials = self.normalize_credentials_to_string(credentials)
+
         url = self.get_request_linked_samples_url(kwargs, definitions)
 
         authenticator_module_name = definitions['module']
@@ -878,6 +881,17 @@ class NonOpenStackApisSamplesGatherer(PollsterSampleGatherer):
 
         return resp, url
 
+    @staticmethod
+    def normalize_credentials_to_string(credentials):
+        if isinstance(credentials, bytes):
+            credentials = credentials.decode('utf-8')
+        else:
+            credentials = str(credentials)
+        LOG.debug("Credentials [%s] were not defined as a string. "
+                  "Therefore, we converted it to a string like object.",
+                  credentials)
+        return credentials
+
     def create_request_arguments(self, definitions):
         request_arguments = super(
             NonOpenStackApisSamplesGatherer, self).create_request_arguments(