tests: don't unlink test image if SKIP_UNLINK set

Don't register a trap to unlink $TMPFILE at the test exit if
SKIP_UNLINK is set.  Otherwise, this makes it difficult to
debug a failing test.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
1 file changed