Fix error when logging exception. (#756)

Reviewed-on: https://git.vdb.to/cerc-io/stack-orchestrator/pulls/756
Co-authored-by: Thomas E Lackey <telackey@bozemanpass.com>
Co-committed-by: Thomas E Lackey <telackey@bozemanpass.com>

stack_orchestrator/deploy/webapp/util.py

@@ -46,7 +46,7 @@ def logged_cmd(log_file, *vargs):
         result.check_returncode()
         return result.stdout.decode()
     except Exception as err:
-        print(result.stderr.decode(), log_file)
+        print(str(err), file=log_file)
         raise err