SR-2856: adapt dispatch_timer_set_time for CI

Adjust the number of 'fast' ticks and the timeout
parameters to make the test much less likely to
be subject to spurious failures in the CI environment.
diff --git a/tests/dispatch_timer_set_time.c b/tests/dispatch_timer_set_time.c
index f7821fc..ff78260 100644
--- a/tests/dispatch_timer_set_time.c
+++ b/tests/dispatch_timer_set_time.c
@@ -51,9 +51,9 @@
 		struct timeval end_time;
 		gettimeofday(&end_time, NULL);
 		// Make sure we actually managed to adjust the interval
-		// duration.  Seven one second ticks would blow past
+		// duration.  Fifteen one second ticks would blow past
 		// this.
-		test_long_less_than("total duration", end_time.tv_sec - start_time.tv_sec, 3);
+		test_long_less_than("total duration", end_time.tv_sec - start_time.tv_sec, 10);
 		test_stop();
 
 		dispatch_release(s);
@@ -61,7 +61,7 @@
 
 	dispatch_source_set_event_handler(s, ^{
 		fprintf(stderr, "%d\n", ++i);
-		if (i >= 7) {
+		if (i >= 15) {
 			dispatch_source_cancel(s);
 		} else if (i == 1) {
 			dispatch_source_set_timer(s, dispatch_time(DISPATCH_TIME_NOW, 0), NSEC_PER_SEC / 10, 0);