Misc ZFS test suite fixes

tests/sys/cddl/zfs/tests/cache/cache_009_pos.ksh
Improve debuggability of this test by dumping pool status
appropriately.

tests/sys/cddl/zfs/tests/compression/compress_002_pos.ksh
tests/sys/cddl/zfs/tests/compression/compression_test.sh
Delete the compress_002_pos testcase.

tests/sys/cddl/zfs/include/libtest.kshlib
create_vdevs(): Remove OBE variable $vdev, which had no effect.
Noticed by Alan.

Submitted by: Will
Sponsored by: Spectra Logic Corp