flux-mini,python,sched-simple: need a way to request exclusive allocation of a node

[SteVwonder]

Problem:

Node-exclusive allocations are a very common allocation request in HPC but are not support by Flux currently. flux-mini has no way to request exclusive allocation of a node. The Jobspec class in the python bindings does not make setting exclusivity for nodes easy. sched-simple does not support satisfying a request with exclusive: true set for a node.

Proposed Solution:

• Update Jobspec V1 RFC25 to support the exclusive: true under the node resource: RFC25: need a way to request exclusive allocation of a node rfc#261
• Update the JobspecV1 class to make setting exclusivity easier
  • Probably either a new method or a new argument to the from_command method
• Update flux-mini to allow requesting resources as exclusive
  • --node-exclusive and --exclusive=node were both mentioned on a coffee call, with the latter being preferred for its generality

[grondo]

This is now possible with flux run --exclusive option.