Address non-deterministic unit test failure

This timer test occasionally fails due to sleep lasting slightly less time than the specified duration. I think this is fundamentally due simply to the relatively sloppy specs on sleep provided by OSes (most are apparently only accurate at the 1-10ms level, and while usually they run long, they can occasionally run short too).

test/unit/tools/test_opttools.py

@@ -49,8 +49,8 @@ def test_timer(self):
         timeDict = {}
         with opt.timed_block('time', timeDict):
             sleep(duration)
-
-        self.assertGreaterEqual(timeDict['time'], duration)
+        lt_tol = 1e-3
+        self.assertGreaterEqual(timeDict['time'], duration-lt_tol) #sometimes sleeps lasts slightly less than specified duration.
         tolerance = 0.2  # this should deliberately be large, for repeatability
         self.assertLessEqual(timeDict['time'], duration + tolerance, "timed block result is greater than {} seconds off".format(tolerance))