exoscale: allow reusing existing SSH key pair
exoscale: allow reusing existing SSH key pair

Signed-off-by: Yoan Blanc <7e8c88beed64bd6a341c3085bc82ac100e832f6e@exoscale.ch>

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