Enable to add/remove nodes from a deployment in update status.

[micafer]

To enable the elastic management of virtual cluster using the CLUES orchestrator plugin it is needed to add this feature to enable to boot more that one node at the same time. Currently we are limited to boot nodes sequentially.

[gmolto]

This issue was raised again by @maricaantonacci during the last WP5 audio. From the CLUES perspective we would need that the Orchestrator allows to perform an operation with an infrastructure while another operation is ongoing with the same infrastructure. Otherwise, the requests made by CLUES are no longer valid and clusters enter an invalid state.

Is this is feasible to be implemented? If not, we will have to figure out how to handle this from the CLUES plugin to avoid weird behaviours.

Regards.

/cc @alpegon