The script name displayed is separated by spaces when the exec job is abnormal;

such as,when i execute 'freezer-agent --action exec --command /home/backup.sh',
reported error:while executing script / h o m e / b a c k u p . s h return code was 1 instead of 0

Change-Id: Iea2f04af8672b3abd4f684b7cb5120a9e1b77cf9

freezer/utils/exec_cmd.py

@@ -49,5 +49,5 @@ def popen_call(sub_cmd, input, is_last_process):
         if rc != 0:
             raise Exception('Error: while executing script '
                             '%s return code was %d instead of 0'
-                            % (' '.join(sub_cmd), rc))
+                            % (''.join(sub_cmd), rc))
     return process