Initial support for provisioning SLE12 nodes

But ```repo_names``` are correctly selected based on target platform version - so it already allows to have separate subdirectories. This is not a case for the repositories stored in provisioner.
/etc/crowbar/provisioner.json does not count with version and usually (I assume) does not point to local/admin node repositories but to e.g. some network one. Use can add e.g. storage product here, which should not be available for all nodes, but e.g. for SLE12 ones.