add ability assert logs

Author: Stepan Neretin

testgres/plugins/pg_probackup2/pg_probackup2/app.py

@@ -124,6 +124,7 @@ def run(self, command, gdb=False, old_binary=False, return_id=True, env=None,
                 def stream_output(stream: subprocess.PIPE) -> None:
                     for line in iter(stream.readline, ''):
                         print(line)
+                        self.test_class.output += line
                     stream.close()
 
                 self.process = subprocess.Popen(