streamline development / testing environment setup

Add two new scripts which aim to ease creation and setup of
a machine for Crowbar admin node installation.

create-vm.sh creates fresh KVM VMs via libvirt.  This can be used to
create both the Crowbar admin node VM and subsequent PXE-booting
Crowbar nodes.

crowbar-prep.sh prepares a host for Crowbar admin node installation.
This takes care of making the required repositories available, and
performs a few other tweaks.  The repositories can be provided via one
of several mechanisms which aim to cover the most common scenarios,
e.g. NFS-mounting from servers in Nuremberg, or from an NFS server on
the VM host, or 9p virtio mounts from the VM host.

These are mainly intended for use with the SUSE Cloud 2.0 kiwi
appliance in the SUSE/cloud github repo:

  https://github.com/SUSE/cloud/tree/master/dev-setup/cloud-2.0/sles11-sp3