Fix string interpolations for Terraform 0.12#1

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Nighthawk14 wants to merge 2 commits intoconnect-group:masterfrom

HappyFerret:master

Commits on Jul 6, 2020

Update string interpolations for terraform >=0.12.0. Update minumum version to 0.12.0
Antoine Savignac
committed
Update variables types to match Terraform >=0.12 requirements
Antoine Savignac
committed