ZTS: Use /dev/urandom instead of /dev/random

Use /dev/urandom so we never have to wait on entropy.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #16442