when up-ing several boxes at once, VBoxManage modifyvm gets cranky and throws random lock errors. this adds the existing retryable logic to
the customize and sane_defaults actions, both of which fire a bunch of
modifyvm commands, all of which are fine to run multiple times.
This starts the transition of replacing VM with Machine. Machine still
isn't ready to fully replace VM but by moving it now, I'm able to find
the spots that need to be fixed. At this point `vagrant status` works
with the new provider interface.
Mitchell Hashimoto
Andy Fowler
Stephan Meissl