Provide the new way to set Hyperv virtual switch instead of the deprecated one

following the tutorial for windows https://developers.redhat.com/products/cdk/hello-world/#fndtn-windows it is mentioned to use HYPERV_VIRTUAL_SWITCH

when launching "minishift start", it is mentioned that using this environment variable is deprecated.

– Check if deprecated options are used ... Use of HYPERV_VIRTUAL_SWITCH has been deprecated Please use: minishift config set hyperv-virtual-switch ExternalVirtualSwitch FAIL