fw/execution: handle error on run initialize

- Use indentcontext inside initialize_run to make sure log level
  is dedented on error.
- Ensure Executor postamble always runs, event if runner errors.
- Fix format_duration() to handle sub-second timedeltas.

wa/framework/execution.py

@@ -352,7 +352,9 @@ class Executor(object):
         self.logger.info('Starting run')
         runner = Runner(context, pm)
         signal.send(signal.RUN_STARTED, self)
+        try:
             runner.run()
+        finally:
             context.finalize()
             self.execute_postamble(context, output)
             signal.send(signal.RUN_COMPLETED, self)
@@ -441,9 +443,8 @@ class Runner(object):
         signal.connect(self._warning_signalled_callback, signal.WARNING_LOGGED)
         self.context.start_run()
         self.pm.initialize()
-        log.indent()
+        with log.indentcontext():
             self.context.initialize_jobs()
-        log.dedent()
         self.context.write_state()
 
     def finalize_run(self):

wa/utils/misc.py

@@ -258,7 +258,7 @@ def format_duration(seconds, sep=' ', order=['day', 'hour', 'minute', 'second'])
             continue
         suffix = '' if value == 1 else 's'
         result.append('{} {}{}'.format(value, item, suffix))
-    return sep.join(result)
+    return result and sep.join(result) or 'N/A'
 
 
 def get_article(word):