Exit on error with proper error format

[chrishulton]

For some reason this was printing errors in a JSON format similar to the issue format and not exiting, leading to the CLI trying to parse the error as an issue and erroring.

Before:

Starting analysis
Running golint: Failed

Analysis failed with the following output:
golint:stable produced invalid output: Category must be at least one of Bug Risk, Clarity,
Compatibility, Complexity, Duplication, Performance, Security, Style; Check name must be pr
esent; Location is not formatted correctly; Path must be relative to the project directory;
 Type must be 'issue' but was 'warning': `{"type"=>"warning", "description"=>"Could not lin
t file (/code/foo.go:1:1: expected 'package', found 'EOF')", "location"=>{"path"=>"/code/fo
o.go"}}`.

After:

Starting analysis
Running golint: Done!
error: (CC::Analyzer::Engine::EngineFailure) engine golint:stable failed with status 1 and stderr
Could not lint file: /code/foo.go
Error /code/foo.go:1:1: expected 'package', found 'EOF'

This makes the engine consistent with gofmt.