Feature/basic json heredoc support

[eerkunt]

This PR introduces ;

• a new helper function where enables support for some heredoc json strings. (Custom Scenarion in encryption at rest feature throws AttributeError #90)
• added aws_emr_security_configuration encryption at rest variables for encryption validations scenarios.

[coveralls]

Pull Request Test Coverage Report for Build 331

• 20 of 20 (100.0%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+3.02%) to 78.65%

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Files with Coverage Reduction	New Missed Lines	%
terraform_compliance/main.py	1	34.0%

Totals
Change from base Build 327:	3.02%
Covered Lines:	501
Relevant Lines:	637

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💛 - Coveralls