Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Testing: add framework for the kernel unit tests.

This changes intends to reduce the bar to the kernel unit-testing by
introducing a new kernel-testing framework ("ktest") based on Netlink,
loadable test modules and python test suite integration.

This framework provides the following features:
* Integration to the FreeBSD test suite
* Automatic test discovery
* Automatic test module loading
* Minimal boiler-plate code in both kernel and userland
* Passing any metadata to the test
* Convenient environment pre-setup using python testing framework
* Streaming messages from the kernel to the userland
* Running tests in the dedicated taskqueues
* Skipping or parametrizing tests

Differential Revision: https://reviews.freebsd.org/D39385
MFC after: 2 weeks

testing: add python test examples

Simplify the adoption of python tests by proving some examples,
utilising commonly-used patterns.

Differential Revision: https://reviews.freebsd.org/D37902
Reviewed by: asomers
MFC after: 2 weeks