Add flag to vagrant up to not destroy VM on error

[aknrdureegaesr]

This connects to #516 and #2010.

The fact that Vagrant burns all traces makes it more difficult than one would like to investigate what goes wrong. In my work on 516, I have already asked you to add the ability to not destroy the VM completely, so one can sift through the rubble.

Your harsh answer to #2010 makes it very clear that you did not investigate contributions to #516 that happened after you closed it. (I did mention which Vagrant version I used.)

On the other hand, I'm not completely giving up on Vagrant yet, as you did express some interest in investigating.

So, to dig out what was hidden somewhere in my work on #516, but clearly needs an issue of its own: If you want to help me help you, kindly add an option to Vagrant so it doesn't burn the traces (destroy the entire machine) when things go wrong.

In particular, I'd like to be able to look at the Virtualbox logs.

[mitchellh]

Renaming the issue to be more clear but this could be good as an additional flag on vagrant up to not destroy on failure.

[mitchellh]

Fixed. New flag: --no-destroy-on-error