Initial support for provisioning SLE12 nodes
Correctly sort the list of available platforms

Here's how we sort it:
  - first the default platform (since it's the default)
  - then linux platforms, alphabetically sorted (and with higher
    versions first)
  - then Windows, with higher versions first
  - finally Hyper-V, with higher versions first
Merge pull request #1128 from rhafer/vuntz-sle12

Initial support for provisioning SLE12 nodes