Extracting validation error from apply dry run output

[laszlocph]

An attempt to treat validation error output the same way as apply output: reducing the noise by only returning the validation error.

Fixes: #277

Note: I'm not sure about the BDD framework used in the project. Let me know if I misuse it

[laszlocph]

Okay, the suite failed as even for the Utils Suite it started a k8s and was doing stuff. I will revisit this later unless you have some pointers how to go with tests. I'm happy to just write a plain golang test without the framework.

[stefanprodan]

@laszlocph writing a test with go stdlib is ok.

[laszlocph]

@laszlocph writing a test with go stdlib is ok.

thanks, I'm done with my changes.

[stefanprodan]

LGTM

Thanks @laszlocph can you please squash all commits.