xfs_scrub_all: localize the strings in the program

Use gettext to localize the output of this program.  While we're at it,
convert everything to f-strings to make it easier for translators to
understand the string.  f-strings introduce a runtime requirement of
Python 3.6, which includes Debian 10 and RHEL 7.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>