Include the option to not reinitialize the MAC address of VirtualBox's VMs

System Info

$ gitlab-runner -b 11.0.0

$ vboxmanage -v 5.2.14r123301

$ vagrant -v Vagrant 2.1.2

Description

When using VirtualBox executor it creates a clone of the VM, and reinitialize the MAC address of the network interface, but when you use Vagrant to provision a Ubuntu Bionic VM (I haven't tested with other OS) and use that VM with GitLab-Runner, it will start with enp0s3 network interface in DOWN state and the build will freeze at "Creating new VM..."

Proposal

Include a option in config.toml to say GitLab-Runner to not reinitialize the MAC address of the VM's network interface.