high: ui_maintenance: Add maintenance [reload] sublevel (bnc#899234)

This adds a new sublevel: maintenance

Commands in this sublevel are only valid when the cluster is in
maintenance mode, or the affected resource is in maintenance mode.

The patch also adds a command "reload" in this sublevel, which
issues the reload command directly to the RA locally on the current
node. If the resource is not running on the current node, the
command fails.