This test tries to background a command that is stored in an undefined variable.  After doing so, it sleeps for 500 seconds then passes unconditionally.  There's nothing in illumos-gate history to suggest that this has ever worked outside of Sun.
Subsequent to submitting this, I found a command rename_dir that is part the test suite.  I'm guessing that's related and as such this is probably the wrong fix.

Verified that I got a clean build (git clean -xdf .; /opt/onbld/bin/nigthtly ../illumos.sh).  zfstest locks up my test vm (zfs-on-zfs deadlock) in multiple places before it reaches the section of the *.run files, so I don't have a practical way of testing them without modifying them.