test: Add a 'make qcheck' target for quicker testing

At present tests are quite slow to run, over a minute on my machine. This
presents a considerable barrier to bisecting for failures.

The slowest tests are the filesystem ones and the buildman --fetch-arch
test. Add a new 'qcheck' target that skips these tests. This reduces test
time down to about 40 second, still too long, but bearable.

Signed-off-by: Simon Glass <sjg@chromium.org>

test/py/tests/test_fs/test_mkdir.py

@@ -11,6 +11,7 @@ This test verifies mkdir operation on file system.
 import pytest
 
 @pytest.mark.boardspec('sandbox')
+@pytest.mark.slow
 class TestMkdir(object):
     def test_mkdir1(self, u_boot_console, fs_obj_mkdir):
         """