Flaky OkHttpClientTransportTest.testClientHandlerFrameLogger

Seeing this a couple of times in the past.

```java
io.grpc.okhttp.OkHttpClientTransportTest > testClientHandlerFrameLogger FAILED
value of : iterable.size()
expected : 1
but was : 2
iterable was: [java.util.logging.LogRecord@27b6524d, java.util.logging.LogRecord@286478b2]
at io.grpc.okhttp.OkHttpClientTransportTest.testClientHandlerFrameLogger(OkHttpClientTransportTest.java:307)
```

https://travis-ci.org/github/grpc/grpc-java/jobs/741247317

Start with io.grpc.okhttp.OkHttpClientTransportTest.testClientHandlerFrameLogger at line 307 and reproduce the failure described in the Travis log. Inspect why the test sometimes observes two LogRecord instances instead of one; done means the test no longer intermittently fails with duplicate records.

Scritto dal modello di indicizzazione a partire dal testo della issue.