ZTS: Add auto-spare tests

ZTS: Add auto-spare tests

The ZED is expected to automatically kick in a hot spare device
when there's one available in the pool and a sufficient number of
read errors have been encountered.  Use zinject to simulate the
failure condition and verify the hot spare is used.

auto_spare_001_pos.ksh: read IO errors, the vdev is FAULTED
auto_spare_002_pos.ksh: read CHECKSUM errors, the vdev is DEGRADE

Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: David Quigley <david.quigley@intel.com>
Closes #6280