Increase tolerance in comon timer tests.

Fire timers slightly earlier, to avoid a possible source of random test
failures where for some reason the safe_sleep() returns before the timer
signal fires.

test/common/testcommon.cpp

@@ -367,8 +367,8 @@ int test(int argc, const char *argv[])
 	TEST_THAT(!t3.HasExpired());
 
 	// Try both ways of resetting an existing timer.
-	t1 = Timer(1000, "t1a");
-	t2.Reset(2000);
+	t1 = Timer(900, "t1a");
+	t2.Reset(1900);
 	TEST_THAT(!t0.HasExpired());
 	TEST_THAT(!t1.HasExpired());
 	TEST_THAT(!t2.HasExpired());