Ayush

+1 can we please make it compatible with signature of `django.core.cache.backends.base.BaseCache#get_or_set`? Because right now this is not a drop in replacement.

``` › terraforming ec2 --tfstate --merge=terraform.tfstate --region=ap-southeast-1 --overwrite /Users/ayush/.gem/ruby/2.3.0/gems/terraforming-0.18.0/lib/terraforming/cli.rb:269:in `tfstate': undefined method `[]' for nil:NilClass (NoMethodError) from /Users/ayush/.gem/ruby/2.3.0/gems/terraforming-0.18.0/lib/terraforming/cli.rb:250:in `execute' from /Users/ayush/.gem/ruby/2.3.0/gems/terraforming-0.18.0/lib/terraforming/cli.rb:50:in `ec2' from /Users/ayush/.gem/ruby/2.3.0/gems/thor-0.20.3/lib/thor/command.rb:27:in `run' from /Users/ayush/.gem/ruby/2.3.0/gems/thor-0.20.3/lib/thor/invocation.rb:126:in `invoke_command' from /Users/ayush/.gem/ruby/2.3.0/gems/thor-0.20.3/lib/thor.rb:387:in...

+1

:+1: