provider/aws: Add JSON validation to the aws_cloudformation_stack resource.

[kwilczynski]

This commit adds support for new helper function which is used to
normalise and validate JSON string.

Signed-off-by: Krzysztof Wilczynski krzysztof.wilczynski@linux.com

[kwilczynski]

Part of work which began in #8028.

[kwilczynski]

Acceptance test is passing:

$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSCloudFormation_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/09/14 23:55:53 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSCloudFormation_ -timeout 120m
=== RUN   TestAccAWSCloudFormation_basic
--- PASS: TestAccAWSCloudFormation_basic (82.33s)
=== RUN   TestAccAWSCloudFormation_defaultParams
--- PASS: TestAccAWSCloudFormation_defaultParams (83.21s)
=== RUN   TestAccAWSCloudFormation_allAttributes
--- PASS: TestAccAWSCloudFormation_allAttributes (178.29s)
=== RUN   TestAccAWSCloudFormation_withParams
--- PASS: TestAccAWSCloudFormation_withParams (151.38s)
=== RUN   TestAccAWSCloudFormation_withUrl_withParams
--- PASS: TestAccAWSCloudFormation_withUrl_withParams (227.25s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    722.481s

[radeksimko]

Probably a nit pick - but looking at the code makes me think we should have a tiny function for this which we could simply reference as StateFunc to avoid the repetition, but I frankly can't think of a good name for such function 💭
and maybe the repetition of 2-3 lines isn't that bad after all.

[kwilczynski]

Good point. I thought about factoring this out, but then I have a wish to replace this with an appropriate DiffSuppressFunc function. Therefore, I would consider these not-there-to-stay long term. Also, I would hope that the compiler is going to inline these... :)

[ghost]

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