fix flaky unit-test CodelTest

Summary:
Sometimes it fails to throw exception in [Codel::setOptions](https://github.com/facebook/folly/blob/master/folly/executors/Codel.cpp#L109), since it failed the check `interval <= delay`.

The reason is that both interval and delay are [POD](https://github.com/facebook/folly/blob/master/folly/executors/Codel.h#L80-L81), thus both are not initialized by default.

Using them without initialization is UB. In x86, they will have random value (since x86 doesn't have trap representation), thus sometimes it passes, sometimes it fails.

Based on comment, it looks like the intention is copying the `options` from default initialized `Codel`.

Reviewed By: amlannayak

Differential Revision: D20499449

fbshipit-source-id: e12de0b42c02a8bf6379ba7fd224e0ae173945f0

folly/executors/test/CodelTest.cpp

@@ -138,7 +138,7 @@ TEST(CodelTest, updateInterval) {
 
 TEST(CodelTest, invalidParamUpdates) {
   folly::Codel c;
-  folly::Codel::Options opts;
+  folly::Codel::Options opts = c.getOptions();
   EXPECT_EQ(milliseconds(5), c.getOptions().targetDelay());
   EXPECT_EQ(milliseconds(100), c.getOptions().interval());