tests: skip running long test with "make check" and add "make fullcheck"

tests: skip running long test with "make check" and add "make fullcheck"

Don't run tests which take longer than 20 seconds to run (especially
f_large_dir, whose run time is well over ten minutes) for "make
check".  The new "make fullcheck" will run all of the regression tests
for e2fsprogs.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>