Updated Fix for #2 - Command palette hang while searching for Vagrantfile

Taking direction from most recent suggestions, this consolidates the Vagrantfile search to just the Vagrant class.  I've tested this on a couple projects, vagrant and non-vagrant, and it seems to be working.

That said, the way I called out to getVagrantConfigPath from VagrantBaseCommand feels like it's wrong to me.  Though, not being a "real" python programmer, I don't know if or how wrong it may be.