zfs: Update test format strings to match variable typtes

And drop stray 'd' from the end of some printed numbers. I assume this
was the result of someone thinking u is a printf length modifier for d,
not a format specifier itself.

Reviewed by: kevans, rew
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34387