Issue: https://github.com/mitchellh/vagrant/issues/8468
A lot of vboxmanage commands are flakey and frequently cause
bringing multiple machines up at once to fail, especially when
the host system is under heavy load. Most commands are also safe
to retry and just result in a no-op, so we can simply add
'retryable' to a lot of existing calls. For the others we need to
do a little bit of cleanup or reevaluate the parameters before
trying again.
2e775e8101