Convert zvol_thrash_001_pos to use gnop(8)

tests/sys/cddl/zfs/tests/zvol_thrash/cleanup.ksh
tests/sys/cddl/zfs/tests/zvol_thrash/setup.ksh
tests/sys/cddl/zfs/tests/zvol_thrash/zvol_thrash.cfg
tests/sys/cddl/zfs/tests/zvol_thrash/zvol_thrash_001_pos.ksh
tests/sys/cddl/zfs/tests/zvol_thrash/zvol_thrash_test.sh
Use gnop(8) to remove providers instead of SAS phy control. This
has several advantages:

• Requires no special hardware
• Works in VMs
• No 2-second delay for the provider to disappear
• Predictable device names during thrash tests
• Simplified logic, especially during cleanup

Also, speed up the test by a factor of two. This is possible
because there's no longer the 2 second delay for a provider to
disappear.

Sponsored by: Spectra Logic Corp