Set persistent ztest failure mode

In order to reliably detect deadlocks in the create and import
path ztest should set the failure mode property. This ensures
that the pool is always using the correct failmode behavior.

Removed insidious use of local variable in MAXFAULTS macro.

Converted VERIFY() to VERIFY0() where appropriate.

Reviewed-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #7111