Support 3 AZs for Terraform 0.11

[pkoraca]

Hello,

Here's PR for Terraform 0.11 support for 3 AZ. Also, terraform-null-label module was bumped since the old version was omitting hyphen character.

[aknysh]

thanks @pkoraca
please run terraform fmt and rebuild README by executing these commands:

make init
make readme/deps
make readme

It will add the new variables and outputs to README.md automatically.

In general, any changes to README should be made in README.yaml (not in this case), and after that executing the commands above will rebuild README.yaml into README.md and add all new variables and outputs to README.md

thanks

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