Module dependency check is not strict enough

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The current module dependency check verifies that the global list of modules is consistent (all required modules are included in the global module list) and that the device-specific requirements are met by each node. It obviously does not check whether a node module list is consistent, or this topology wouldn't make it through (causing #466 as a side effect):

defaults.device: eos

nodes:
  r1:
    module: [ vlan, vxlan ]
  r2:
    module: [ vxlan ]