Add e2e testing framework

[concaf]

We know that every Kedge spec definition in https://github.com/kedgeproject/kedge/tree/master/examples and https://github.com/kedgeproject/kedge/tree/master/docs/examples is valid. We need a testing framework that gets all the YAML files from these 2 locations and runs the schema validation on them.
Any PR should only be merged if these tests pass on Travis.

Results from #17 (comment)

ping @surajnarwade @surajssd

[surajnarwade]

I will take this up

[surajssd]

There are 2 different things here, here we are assuming all examples are valid and testing if the change in schema is valid.

On Kedge repo the same code will assume schema is valid and test if the change in examples are valid.

[concaf]

Yes.