jw.pkg.lib: Don't log {e}

Don't log an Exception as {e} but as str(e) producing nicer output.
Or as repr(e) if a backtrace is requested, because to people who can
read backtraces, type info might be of interest. Also, remove
pointless time stamps, those belong into the logging framework.

Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/App.py

@@ -116,10 +116,7 @@ class App: # export
         try:
             ret = await self._run(self.__args)
         except Exception as e:
-            if hasattr(e, 'message'):
-                log(ERR, e.message)
-            else:
-                log(ERR, f'Exception: {type(e)}: {e}')
+            log(ERR, repr(e) if self.__back_trace else str(e))
             exit_status = 1
             if self.__back_trace:
                 raise