buildman: Make test_process_limit handle time.monotonic()

Newer versions of filelock use time.monotonic() instead of time.time().
Update the test the handle this.

It would be better if filelock had support for writing unit tests which
use locking.

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

tools/buildman/test.py

@@ -779,6 +779,7 @@ class TestBuild(unittest.TestCase):
         tmpdir = self.base_dir
 
         with (patch('time.time', side_effect=self.get_time),
+              patch('time.monotonic', side_effect=self.get_time),
               patch('time.sleep', side_effect=self.inc_time),
               patch('os.kill', side_effect=self.kill)):
             # Grab the process. Since there is no other profcess, this should