Run tests on both k10 and net45

Third time's a charm...

@davidfowl @loudej Would you mind glancing through this? I modified the k task to take an optional runtime parameter. If specified, it basically does a k list and picks one with the specified runtime and the same version and architecture as the active one.
curious: commands assume `k` is in the path.  so why not assume `kvm` is in the path?