Import atf 0.22 snapshot ca73d08c3fc1ecffc1f1c97458c31ab82c12bb01

This includes improvements to the atf-sh helper functions that
significantly reduce the number of spawned processes for each test
and therefore speeds up running the testsuite noticeably.

(cherry picked from commit c203bd70b5957f85616424b6fa374479372d06e3)