Group virtual machines in VirtualBox.

See http://blog.kennyrasschaert.be/blog/2013/05/07/grouping-vagrant-machines-in-virtualbox/
Set `--cpuexecutioncap` for VirtualBox
Upgraded `puppetlabs/mysql` module to v2.2.1
Specify the minimum version for vagrant
`Vagrant.require_version` requires v1.4.0
Revert "Use the `vagrant-auto_network` plugin."

This reverts commit 9894dea92283bf424c1f72e7c0ffa5de53b8f40b.

This plugin doesn't work on Vagrant v1.4.x (see https://github.com/adrienthebo/vagrant-auto_network/issues/4).
Use the `vagrant-vbguest` plugin to update "VirtualBox Guest Additions" on the virtual machine.
Disabled the `vagrant-cachier` plugin.

See https://github.com/fgrehm/vagrant-cachier/issues/76