ZTS: alloc_class.ksh must wait for the process to exit
The alloc_class_* tests may fail on Linux with an EBUSY error if
`zfs destroy` is run before the `dd` process has had a chance to
terminate. Wait on the pid after the `kill -9` to make sure.
When testing I didn't observe any failures for the alloc_class
tests. Remove them from the exceptions list, the CI was used to
verify the tests pass on all platforms.
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Rich Ercolani <rincebrain@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #12873