MDEV-654 Assertion `share->now_transactional' failed in flush_log_for_bitmap on concurrent workload with Aria tables

I was able to repeat the problem with old version of randgen

Reason for crash:

- It's not safe to change share->now_transactional if there are changed
bitmaps in the pagecache as flushing these can cause redo-entries and
the bitmap flush code checks that share->now_transactional is set.

Fixed by flushing bitmaps in _ma_tmp_disable_logging_for_table() before
we set share->now_transactional to 0