[#2604] Not try to use sun.misc.Cleaner when on android

Motivation:

When a user tries to use netty on android it currently fails with "Could not find class 'sun.misc.Cleaner'"

Modification:

Encapsulate sun.misc.Cleaner usage in extra class to workaround this isssue.

Result:
Netty can be used on android again
Remove the deprecated methods in SPDY and HTTP

No need to keep ABI compatibility since we are working on a
backward-incompatible branch
Enable verbose:gc only when 'leak' profile is disabled

The leak profile generates a lot of garbage which makes the verbose:gc
output too large.
Upgrade JACOCO to the latest version

.. to fix the build errors triggered by the old JACOCO release
[#2615] Correctly update SelectionKey after selector rebuild

Motivation:

When a select rebuild was triggered the reference to the SelectionKey is not updated in AbstractNioChannel. This will cause a CancelledKeyException later.

Modification:

Correctly update SelectionKey reference after rebuild

Result:

Fix exception
Let EpollReuseAddrTest also work with kernel versions that not have bugfix release part
Cleanup comment / code
fix example missing break statement in ReplayingDecoder
Correct a JavaDoc typo
Maintain decoder result in HttpObjectAggregator

Motivation:
DecodeResult is dropped when aggregate HTTP messages.

Modification:

Make sure we not drop the DecodeResult while aggregate HTTP messages.

Result:

Correctly include the DecodeResult for later processing.
Fix compile error