[Python3] Adds bytes to str conversion management

On RHEL8 with Python3, the template's contents returned by the Swift
client get_object method is byte object and need to be converted into a
string.

Change-Id: Ia35abb66b9e61a7154406cf83c6da1e68a2f96b7
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>
(cherry picked from commit f144be5bcc)

lookup_plugins/tht.py

@@ -41,6 +41,11 @@ class LookupModule(LookupBase):
         container = swift.get_container(variables['plan'])
         for item in container[1]:
             obj = swift.get_object(variables['plan'], item['name'])
+            try:
+                obj = (obj[0], obj[1].decode('utf-8'))
+            except AttributeError:
+                pass
+
             if os.path.splitext(item['name'])[-1] not in EXCLUDED_EXT:
                 ret.append((item['name'], obj))