Introduce slowdown factor for unit test deadlines

Dramatically lowers (eliminates maybe?) false negatives from ?SAN runs.
diff --git a/test/core/end2end/tests/cancel_before_invoke.c b/test/core/end2end/tests/cancel_before_invoke.c
index 0ab9ac6..6e100db 100644
--- a/test/core/end2end/tests/cancel_before_invoke.c
+++ b/test/core/end2end/tests/cancel_before_invoke.c
@@ -61,7 +61,7 @@
 }
 
 static gpr_timespec n_seconds_time(int n) {
-  return gpr_time_add(gpr_now(), gpr_time_from_micros(GPR_US_PER_SEC * n));
+  return GRPC_TIMEOUT_SECONDS_TO_DEADLINE(n);
 }
 
 static gpr_timespec five_seconds_time(void) { return n_seconds_time(5); }
@@ -103,7 +103,8 @@
 }
 
 /* Cancel before invoke */
-static void test_cancel_before_invoke(grpc_end2end_test_config config, int test_ops) {
+static void test_cancel_before_invoke(grpc_end2end_test_config config,
+                                      int test_ops) {
   grpc_op ops[6];
   grpc_op *op;
   grpc_call *c;