[PE-1788] Use safe_yaml for report parsing

This patch changes the report parsing code to use safe_yaml to prevent security vulnerability. As safe_yaml deserializes into basic data types only, further changes were needed to transform the deserialized data into structure expected by the original code.

Notice:
- `safe_yaml` gem needs to be packaged
- `spec/fixtures/reports/puppet26/resource_status_test.yaml` originally contained 2 reports. That was causing RSpec instabilities so I removed the first report from the file. I suppose it was not there on a purpose.