Detect vagrant boxes with custom vagrantfile name

[siarhei-makarevich]

There is no functionality at the moment to fork with boxes which use custom names for vagrant file and dot file.

f.e. im using it to place two separate box in the same directory and run them with command

VAGRANT_VAGRANTFILE=Vagrantfile.centos6 VAGRANT_DOTFILE_PATH=.vagrant_centos6 vagrant up
VAGRANT_VAGRANTFILE=Vagrantfile.centos7 VAGRANT_DOTFILE_PATH=.vagrant_centos7 vagrant up

Because of vagrantfiles have different name then "Vagrantfile", Vagrant Manager doesn't detect that boxes. Also Vagrant Manager don't have functionality to configure name of Vagrantfile.