(maint) Fix up Solaris acceptance test (don't output to stderr)
(#23377) Fix parsing of 'zfs -?' stdout to allow zfs version detection

Facter detects zfs version by first running 'zfs -?' to verify that it
can call 'zfs upgrade -v' safely. Prior to this patch, the parsing
of the output of 'zfs -?' assumed a different (earlier?) format for the
output of 'zfs -?' and thus would miss that the 'zfs upgrade' sub-command
is in fact supported.

This patch loosens the regex so that 'upgrade' doesn't have to be the
first word on a line, and also adds a new fixture to match the
current output of 'zfs -?'.
Merge branch 'pr/571'

* pr/571:
  (#23377) Fix parsing of 'zfs -?' stdout to allow zfs version detection
  (maint) Fix up Solaris acceptance test (don't output to stderr)

Closes GH-571