vagrantutil: queue box builds

[rjeczalik]

Having concurrent vagrant up does not work for all the boxes, especially those which use bridge networking, as VirtualBox commands executed conflict with each other.

VagrantUp implementation should queue all the builds and provide API for getting state.

This fixes the following failures:

2016-11-18T08:48:38.549Z DEBUG    [vagrantutil    ][PID:24168][logging/context.go:53] [/Users/rjeczalik/.vagrant.d/koding/team/urtv907ed4f2] An action 'up' was attempted on the machine 'default',
2016-11-18T08:48:38.549Z DEBUG    [vagrantutil    ][PID:24168][logging/context.go:53] [/Users/rjeczalik/.vagrant.d/koding/team/urtv907ed4f2] but another process is already executing an action on the machine.
2016-11-18T08:48:38.549Z DEBUG    [vagrantutil    ][PID:24168][logging/context.go:53] [/Users/rjeczalik/.vagrant.d/koding/team/urtv907ed4f2] Vagrant locks each machine for access by only one process at a time.
2016-11-18T08:48:38.55Z  DEBUG    [vagrantutil    ][PID:24168][logging/context.go:53] [/Users/rjeczalik/.vagrant.d/koding/team/urtv907ed4f2] Please wait until the other Vagrant process finishes modifying this
2016-11-18T08:48:38.55Z  DEBUG    [vagrantutil    ][PID:24168][logging/context.go:53] [/Users/rjeczalik/.vagrant.d/koding/team/urtv907ed4f2] machine, then try again.