Made compute zone name generic

[metonymic-smokey]

Refers to issue #1296
Changed file to make compute zone reference generic and added a note about regional clusters.

[metonymic-smokey]

@consideRatio here's the PR.
I've tried to follow the first part of #1296 while adding to the docs.
Should I also add a note about the second part ?

Thanks!

[metonymic-smokey]

@consideRatio any idea why it's not passing the Travis CI check?

[metonymic-smokey]

@willingc made the changes you suggested! Thanks a lot!

[consideRatio]

Sorry for slow feedback about this PR! If we introduce the concept of regional clusters, I'd like to see some additional understanding presented as well.

• If you create a regional cluster, you will by default create nodes in at least three zones.
• If you create a regional cluster, you will always get High Availability (HA) on your k8s api-server for free. This means that kubectl get pods for example should keep working no matter if an individual api-server is being upgraded which they automatically are sometimes.
• If you want to reap the benefit of a HA k8s api-server while not tripling the amount of nodes, you can limit your own servers to one single zone by using the --node-locations flag and specifying a specific zone, such as us-central1-a:

[metonymic-smokey]

@consideRatio thanks for the review!
Apologies for the very brief PR.
I shall add these points too!

[metonymic-smokey]

@consideRatio sorry for the delay!
Added the points you had asked for, referring to the official GCP docs and blog.
Any changes I need to make to this?
Thanks!

[metonymic-smokey]

@willingc @consideRatio would love it if you could review this PR!
Thanks!

[consideRatio]

Thanks for your work on this ❤️! I made some suggestions, if they look good to you it all LGTM!

[metonymic-smokey]

@consideRatio the changes look good. Added the changes with a couple of minor fixes.

[consideRatio]

Thank you for this thorough work @metonymic-smokey! ❤️ 🎉