LU-18276 tests: add debugging to sanity-pfl/16b

LU-18276 tests: add debugging to sanity-pfl/16b

Add extra debugging messages to sanity-pfl.sh test_16b to help find
what is causing this test to fail with ENOSPC intermittently.

Reduce size of overstriped PFL file layout slightly, so that two
such components can fit within the xattr size limit, which may or
may not be the cause of the ENOSPC failures.

Print a message in llapi_layout_file_open() if ENOSPC is hit, so
that we can determine the xattr size, in case it is too large.
Move layout conversion before file open() to avoid contacting
MDS needlessly if the layout is bad.

Test-Parameters: trivial testlist=sanity-pfl env=ONLY=16b,ONLY_REPEAT=100
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Iaf347e231147041dda07277227e80f0b6f2540e5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59416
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Emoly Liu <emoly@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>