Merge branch 'master' into 'master'

Merge branch 'master' into 'master'

makebuildserver: support running VirtualBox in a VM

For debian.jenkins.net, our test environment is a kvm instance that does not expose the hardware virtualization instructions.  So this auto-detects whether the current machine, virtual or not, supports the hardware virtualization.  If not, it uses VirtualBox's software emulator, which should run everywhere, even in a kvm instance.

See merge request !108