Add warning/confirmation before powering off a node

[srcshelton]

Is your feature request related to a problem? Please describe.

As an end-user of a TP2 system making use of installed nodes for long-running compute tasks,
I would like the certainty of being protected from accidentally powering-off a running node or the wrong node)
in order to minimise any time/work lost if a node is incorrectly powered-down.

Describe the solution you'd like

When the BMC Web UI 'Power' view is used to un-tick a node, there should be some form of confirmation before the power to that node is cut.

Ideally, the ticks on this page would be standard check-box controls, and there would be a separate "Apply" button. On hitting "Apply", a confirmation dialog would be shown confirming what actions will be performed if allowed to continue, as well as giving an option to back-out. This would also allow several nodes to be turned on or off at once.

Describe alternatives you've considered

Alternatively, if a two-stage select-then-apply approach isn't desired, at least a confirmation dialog being shown when powering-down a node would be much safer. Note that confirmation could reasonably be skipping when powering-on a node which is currently off.

[srcshelton]

(If node monitoring as per #170 is implemented then any warning on attempting to power-cycle a node marked as failed could also skip the confirmation dialog?)

[svenrademakers]

fixed in e5f6158 and upwards