If the root account is configured to use a different shell than sh,
it fails to retreive the pid of the background process.
Approved by: des
Obtained from: chs
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D36930
renice_abs_user and renice_rel_user tests modify global state, so they
are not compatible with parallel execution.
Reviewed by: asomers
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D36720