Vagrant commands handle rate limits instead of failing

[eschoeller]

Is your feature request related to a problem? Please describe.
Yes, 'vagrant up' and 'vagrant box add' both can fail with a status code 429

Describe the solution you'd like
When your software receives a 429, with x-hcp-vagrant-limit-retry-after set, your clients should then automatically wait until that time to retry the operation, instead of failing.

Describe alternatives you've considered
I'm currently making a work-around myself, but it would be nice if your software could handle the retry internally based upon the 429 code coming back.

Additional context
That's it, thanks!