The node offline/mcpu is identical to hbal's setNodesStatus, so let's
move that to CLI.hs and reuse it in hspace (also, rename it and drop
one 's').

Also, the check for the number of nodes is obsolete, as we compute
that from the disk template.

The patch does a bit of other small cleanups.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>