bootstrap: Script to prepare a lokocfg

[pothos]

The prepare.sh script generates a lokocfg file and runs lokoctl to create the cluster. By default it uses the QEMU mode where it creates two bridges (one external and one internal) and QEMU VMs that PXE-boot. For real hardware it requires an interface to be specified where the internal L2 network is, and the MAC addresses of the servers and the BMCs in this internal L2 network.

It uses a lokoctl binary from: https://github.com/kinvolk/lokomotive/pull/1333

[pothos]

Updated it now:

• qemu-script: Use a second bridge for an internal network In the final setup we can use an internal L2 network and don't need to rely on ipvlan. This makes the QEMU setup resemble the final setup but still keeps the PXE/DHCP server on the host system, not in a VM. The required lokoctl binary comes from kinvolk/lokomotive#1317

[pothos]

Made one more change:

• qemu-script: Use a default subnet and no ipvlan interface
  Instead of picking a subnet we can define one and make it configurable in case of conflict. Since we know the subnet we can directly assign it for the QEMU bridge and also remove the ipvlan interface for matchbox.

[pothos]

If run with USE_QEMU=0 and the right config files it can create a cluster on the hardware, too.