Support additional gcloud create instance arguments

[supersteves]

For example we need to enable the display device on our windows VMs, necessary for automated UI tests. This seems like a common requirement for TeamCity.

See --enable-display-device here:
https://cloud.google.com/sdk/gcloud/reference/compute/instances/create#--enable-display-device

We can't solve this using instance templates; Google do not yet support this configuration in instance templates. No sign of that happening:
https://issuetracker.google.com/u/1/issues/133047176

(There are other options we might want, like local SSD, or E2 machine types - but these can be solved with instance templates although it's not so convenient).

[tolache]

Apparently, you can enable a display device in instance templates now: