Update to HTTP/2 Draft 15.
Merge pull request #1162 from square/jw/http-2-draft-15

Update to HTTP/2 Draft 15.
Avoid hardcoding the custom header prefix so the test uses the Platform value

The test is failing under Android CTS tests. Android uses an "X-Android"
prefix.

This fix is benign and ensures the test passes in all cases.
Prevent MockSpdyPeer interfering with Android tests

On Android we run the OkHttp tests as an instrumented test case.
The default UncaughtExceptionHandler on Android will quit the
app, causing the current test to fail.

MockSpdyPeer creates a thread that fails for various reasons
that are not related to / required for the actual test. Often the
exception is thrown during a subsequent test.

This change logs the exception but prevent it from
propagating out of the top of the call stack. This decreases
overall flakiness.
Merge pull request #1168 from nfuller/FixTestOnAndroid3

Avoid hardcoding the custom header prefix
Merge pull request #1170 from nfuller/FixTestOnAndroid5

Prevent MockSpdyPeer interfering with Android tests