tests: report if a test is taking a long time

tests: report if a test is taking a long time

Print out a message if a test takes longer than 60s, with a
reminder to potentially add is_slow_test to that test, so
that it is easier to find which tests are taking a long time,
especially if running with "make -j check" or similar.

Add an exclusion for r_expand_full on MacOS since HFS+ does
not support sparse devices and doesn't like large test images.

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