Add some ATF tests for ctladm

So far only "ctladm port -c" and "ctladm port -r" are covered.

Sponsored by: Axcient
Reviewed by: mav
Pull Request: https://github.com/freebsd/freebsd-src/pull/1279

(cherry picked from commit 9747d11d91642cb9b81602d88e8aebeb388543c7)

Fix mtree entry for ctladm tests

Sponsored by: Axcient

(cherry picked from commit 81ef0a89fcc055bdf3d0f1affbadb643412ebce9)

ctladm: add a copyright header to the port test

[skip ci]

Reported by: markj
Sponsored by: Axcient

(cherry picked from commit a1608e8854da7f3b5734c2fcb85dd740733a08e6)