Add a pre check to avoid deploying a node using the IP of an already deployed node

[thomasdanan]

Component:

'salt', 'ui'

Why this is needed:

The administrator may (by mistake) create a Nde specification using the IP of an already deployed node. When deploying such node, this leads to failure and may have an impact on salt-minion and key negotiation

What should be done:

When adding a node, from the UI or from the CLI, we should check that the IP to reach the node is not already referenced in the Nodes that are already part of the cluster.

Implementation proposal (strongly recommended):

Test plan: