Add --google-min-cpu-platform option for machine creation

Adds --google-min-cpu-platform option for machine creation command.

Example usage:

$ docker-machine create \
                 --driver google \
                 --google-project [PROJECT ID] \
                 --google-min-cpu-platform 'Intel Skylake' \
                 test-machine-name

Binary compiled for Linux amd64 can be found at https://gitlab.com/gitlab-org/ci-cd/docker-machine/-/jobs/131350952/artifacts/file/bin/docker-machine.

Pleas read gitlab-org/release/framework#43 for more details about why it's needed and why we've decided to go this way.

Closes #3 (closed)