Improve error message for failed deployments

[zaro0508]

I'll see the below error messages in my sceptre deploy log however it doesn't tell me which file contains the error. It would be great if sceptre could provide a little more info in these situations. I I tried using the sceptre --debug flag however that didn't provide anymore info.

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[2020-04-27 08:18:01] - prod/sc-product-ec2-linux-jumpcloud sc-product-ec2-linux-jumpcloud AWS::CloudFormation::Stack UPDATE_COMPLETE
"An error occurred (ValidationError) when calling the CreateStack operation: Template format error: unsupported structure."

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[2020-04-27 08:46:42] - prod/sc-product-ec2-linux-jumpcloud sc-product-ec2-linux-jumpcloud AWS::CloudFormation::Stack UPDATE_COMPLETE
"An error occurred (ValidationError) when calling the CreateStack operation: Template format error: YAML not well-formed. (line 44, column 7)"

[ngfgrant]

Error handling is something that has come up in #640 and #564.

I think my suggestion in #640 is probably breaking but could be evolved?