Validate API examples. Rename files

> Actually, the len(files) == len(expected) would catch this. This https://github.com/marianitadn/origin/blob/test-examples/examples/examples_test.go#L128 already compares the file names.

[The for loop](https://github.com/marianitadn/origin/blob/test-examples/examples/examples_test.go#L116-L130) checks one way: if all the files on the disk have an associated rule defined in the `expected` map. But if you define a map key-value where the key - file doesn't exist on the disk it will not raise an error. We can check the length, **after** we check that each file on the disk was associated with a key in the `expected` map, but we will not known which files are missing.