rc/tests: Skip oomprotect tests in a jail

oomprotect cannot be used in a jail.

Reviewed by: bnovkov, christos, markj
Approved by: bnovkov (mentor), christos (mentor), markj (mentor)
MFC after: 1 week

(cherry picked from commit 6fa42b91ca3f481912af98c4d49c44507eb1b8e1)