[hyperv] if no vswitch is specified, only pick the first external one
[hyperv] if no vswitch is specified, only pick the first external one

Signed-off-by: Dowideit, Sven (O&A, St. Lucia) <2bcfa84078a2bb43f2a5eaba37e593306987cb42@csiro.au>

dgageot/machine,exoscale/docker-machine,docker/machine,ibuildthecloud/machine,dweomer/docker-machine,exoscale/docker-machine,ibuildthecloud/machine,dgageot/machine,dweomer/docker-machine,docker/machine