Revert "[#2762] Not expand ByteBuffer[] in ChannelOutboundBuffer"

This reverts commit 8cfc64fa1d665960cd287d05e1148881897fcbdb as it may cause problem if a CompositeByteBuf has more then 1024 components.
Update TrafficShapingTest for Master

Motivation:
Master test seems not ok as in 4.1 in some tests so relax the internal time check but keeping the outside check.

Modifications:
Comment the assertTrue regarding the internal time test and extending to 15s the tests using Exec.

Result:
No more false negative tests (until Master is stable enough to recheck the condition of validation).
Pluggable algorithm to choose next EventLoop

Motivation:

Currently when a new event loop is needed to register a channel our EventLoopGroup implementations just
use a round-robin like algorithm to choose the next event loop. Unfortunately this is not always good
enough as different event loops may become more busy than others over time. This is especially true when
an application handles different kinds of connections (long-living and short-living). This change allows
developers to plug in their own algorithms to choose the next event loop and to collect metrics about the
busyness of the event loops. See #1230

Modifications:

- TODO

Result:

- Developers can plug in their own algorithms into MultithreadEventLoopGroup constructors.
- Developers can gather metrics/feedback from the event loops and use the data in their custom algorithms.