Don't panic when we get ZPOOL_STATUS_NON_NATIVE_ASHIFT
while listing importable pools.

MFC after:	3 days
Per the resolution of POSIX bug 0000779 (note 0002050) add support for using 'i'
as a case insensitive flag.

PR:		standards/184641
Requested by:	David A. Wheeler <dwheeler@dwheeler.com>
MFC After:	1 week
Add regression test for recently added 'i' flag in r259132.

PR:	standards/184641