FUSE directory left mounted in sharness test #5111
Description
While working on a (very defective) PR (#5109) that is causing a sharness test to fail, I couldn't rerun the test due to a FUSE-related error: if I understand correctly (probably not) some directory is left mounted and the test cannot remove it when it starts. I also cannot remove it, and it wasn't evident (at least to me) that this had anything to do with FUSE until I googled the error and found out that I had to manually unmount the directories (which is now what I'm doing as part of the test command to be able to rerun it every time).
./t0040-add-and-cat.sh -v -i
# The test works, it stops before the end because of a failed test (`-i` flag).
# (Something similar happens if I Ctrl+C in the middle of it.)
# I now cannot run again the same test:
./t0040-add-and-cat.sh -v -i
# rm: cannot remove 'trash directory.t0040-add-and-cat.sh/ipns/QmepVq1AZF4FNoopEujVBSofw8syTe4g6tNXswL74Lm9V9': Input/output error
# rm: cannot remove 'trash directory.t0040-add-and-cat.sh/ipfs': Device or resource busy
# FATAL: Cannot prepare test area
# I can't simply remove the directory:
rm trash\ directory.t0040-add-and-cat.sh/ -rfv
# rm: cannot remove 'trash directory.t0040-add-and-cat.sh/ipns/QmepVq1AZF4FNoopEujVBSofw8syTe4g6tNXswL74Lm9V9': Input/output error
# rm: cannot remove 'trash directory.t0040-add-and-cat.sh/ipfs': Device or resource busy
# I have to (manually) unmount to continue testing:
sudo umount -l trash\ directory.t0040-add-and-cat.sh/ipns/
sudo umount -l trash\ directory.t0040-add-and-cat.sh/ipfs/
./t0040-add-and-cat.sh -v -i
# Now it works