xfstests: refactor dump test argument parsing

xfstests: refactor dump test argument parsing

The dump and restore helper functions all call the same _parse_args()
function. xfsdump and xfsrestore have some common options, but others
have different meanings/syntaxes or only exist in one program or the
other. Split _parse_args() into dump and restore variants.

Further, a test cannot pass most options to xfsrestore because many of
the parsed args are not used by the restore helper functions.  Change
the helpers so that the parsed options are available (to be used in
future tests).

Also add a check for a missing --multi argument, and change a couple of
callers to be consistent and use $* instead of "$@".

Signed-off-by: Bill Kendall <wkendall@sgi.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>