Skip VMs without states defined in salt top file _only_ when executing operation using that top file

[marmarek]

Currently qubesctl tool skip VMs for which top file is empty (it checks state.show_top id=VMNAME). It is sensible for state.highstate which would do nothing, but break usage of other commands, like giving state to apply from command line (state.single, state.apply, state.sls...), or even directly calling some salt module.