2021-August-30 - Prerelease - 2.6.350

Infrastructure fixes & use mitogen (#9551)

- fix ansible.cfg config to actually use mitogen
- add group_var/all config to use python3 explicitly. Otherwise mitogen uses python2
- fix flyway tasks, deploy conf file, put password in a file so that it is not
  in the 'cmd'. This allows us to show logging, useful if the task fails (though
  that also prints the cmd, hence having password in a file fixes this)
- update ansible.cfg to use 'yaml' output, provides much nicer output in the case
  of failure or if '--verbose' output is used.
- Fix up flyway role and fix vagrant inventory to pick up group_vars