Added test for being able to read various variants of zstd

As detailed in #12022 and #12008, it turns out the current zstd
implementation is quite nonportable, and results in various
configurations of ondisk header that only each platform can read.

So I've added a test which contains a dataset with a file written by
Linux/x86_64 and one written by FBSD/ppc64.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #12030