Add additional instructions to set OSM_HOSTNAME in case of ClientException

Change-Id: I7b303737e0b7a19e442f84d80544384abee3671b
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>

osmclient/scripts/osm.py

@@ -369,6 +369,9 @@ def cli():
         )
     except ClientException as exc:
         print("ERROR: {}".format(exc))
+        print(
+            'Maybe "--hostname" option or OSM_HOSTNAME environment variable needs to be specified'
+        )
     except (FileNotFoundError, PermissionError) as exc:
         print("Cannot open file: {}".format(exc))
     except yaml.YAMLError as exc: