Fix behavior of gscloud-server-create --password

[bkircher]

In gscloud-server-create, --password is mandatory when creating with storage. This is not enforced by gscloud but API calls fail if user forgets to give a PW. Actually this is fine but annoyingly late.

Second thing is that --password is not used at all when --with-template is not given. Also makes sense since we don't need to set a root PW if we don't create a new storage from a OS template. But again, this is annoyingly silent on this user "error".

Lastly, maybe we just should remove --password flag oand not allow the user to set passwords themselves. For one thing, thse passwords wouldn't be recorded by shell history anymore (good) and user cannot forget to specify one (good). We could use something like https://github.com/sethvargo/go-password to always generate sufficiently secure passwords and return them after the server (erm, storage) has been created.