xfs/444: fix agfl reset warning detection for small log buffers

Collectively, the ten subtests in xfs/444 can generate a lot of kernel
log data.  If the amount of log data is enough to overflow the kernel
log buffers, the AGFL reset warning generated by fix_start and fix_wrap
might have been overwritten by subsequent log data.  Fix this by
checking for the reset warning after each test and only complaining if
at the end if we have /never/ seen the warning.

Found by running on a kernel configured with CONFIG_LOG_BUF_SHIFT=14
(16K).  This happened to be a Raspberry Pi, but in principle this can
happen to anyone.  I'd never noticed this before because x86 helpfully
sets it to 17 (128K) by default.

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