ZTS: Improve redundancy test scripts

• Add additional logging to provide more information about why the test failed. This including logging more of the individual commands and the contents and differences of the record files on failure.

• Updated get_vdevs() to properly exclude all top-level vdevs including raidz3 and draid[1-3].

• Replaced gnudd with dd. This is the only remaining place in the test suite gnudd is used and it shouldn't be needed.

• The refill_test_env function expects the pool as the first argument but never sets the pool variable.

• Only fill the test pools to 50% of capacity instead of 75% to help speed up the tests.

• Fix replace_missing_devs() calculation, MINDEVSIZE should be MINVDEVSIZE.

• Fix damage_devs() so it overwrites almost all of the device so we're guaranteed to damage filesystem blocks.

• redundancy_stripe.ksh should not use log_mustnot to check if the pool is healthy since the return value may be misinterpreted. Just perform a normal conditional check and log the failure.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #11906