Make sure VAGRANT_DOTFILE_PATH is set correctly

[grtjn]

See PR from @miguelrgonzalez, things go wrong if you run vagrant up from a different path..

[grtjn]

Reason why:

Vagrant by default saves VM info in a .vagrant/ folder next to where Vagrantfile lives. You can however start vagrant from a subfolder, in which case VM info from different VMs could get mixed up. Make sure to put .vagrant/ in CWD rather than next to Vagrantfile if there is no Vagrantfile in CWD.

Details about ENV variables: http://docs.vagrantup.com/v2/other/environmental-variables.html