mysql-test/include/maria_empty_logs.inc:
  move mysqladmin call to include file for reusal (so that others don't have to hit the same bug in their tests);
  this include file additionally waits for disconnection. Reasons for BUG#41102:
  - in maria-no-logging.test, we shut down mysqld in maria_empty_logs.inc, remove logs, tell mtr that it can
  restart mysqld, then wait for being connected (wait_until_connected_again.inc), then send commands to new mysqld.
  - but under Windows "mysqladmin shutdown" does not wait for mysqld to be down, so we accidentally removed logs
  while it was shutting down, wait_until_connected_again found that we were connected (because it was shutting
  down slowly, connections were not yet broken), sent new commands, and one of them failed because mysqld finally
  closed connections.
  - the fix is to just wait for disconnection after shutdown.
  - in a sense, the catch is the "again" in wait_until_connected_again.inc...
mysql-test/include/mysqladmin_shutdown.inc:
  shutdown with mysqladmin AND waiting for shutdown to complete (needed on Windows)
mysql-test/include/wait_until_connected_again.inc:
  comment
mysql-test/include/wait_until_disconnected.inc:
  script which waits until connection is lost