[#2308] Use SelectorProvider.open*() to open NIO channels and so remove condition when create new NIO channels.

Motivation:
At the moment we use SocketChannel.open(), ServerSocketChannel.open() and DatagramSocketChannel.open(...) within the constructor of our
NIO channels. This introduces a bottleneck if you create a lot of connections as these calls delegate to SelectorProvider.provider() which
uses synchronized internal. This change removed the bottleneck.

Modifications:
Obtain a static instance of the SelectorProvider and use SelectorProvider.openSocketChannel(), SelectorProvider.openServerSocketChannel() and
SelectorProvider.openDatagramChannel(). This eliminates the bottleneck as SelectorProvider.provider() is not called on every channel creation.

Result:
Less conditions when create new channels.
Remove sniffer whitelist entries for NIO.2

Motivation:
Cleanup pom.xml file.

Modifications:
Remove sniffer whitelist entries for NIO.2 as we not include a NIO.2 bases transport anymore.

Result:
Less entries in pom.xml
[#2307] Remove synchronized bottleneck in SingleThreadEventExecutor.execute(...)

Motivation:
Remove the synchronization bottleneck in startThread() which is called by each execute(..) call from outside the EventLoop.

Modifications:
Replace the synchronized block with the use of AtomicInteger and compareAndSet loops.

Result:
Less conditions during SingleThreadEventExecutor.execute(...)
Fix limit computation of NIO ByteBuffers obtained via ReadOnlyByteBufferBuf.nioBuffer

Motivation:

When starting with a read-only NIO buffer, wrapping it in a ByteBuf,
and then later retrieving a re-wrapped NIO buffer the limit was getting
too short.

Modifications:

Changed ReadOnlyByteBufferBuf.nioBuffer(int,int) to compute the
limit in the same manner as the internalNioBuffer method.

Result:

Round-trip conversion from NIO to ByteBuf to NIO will work reliably.
[#2305] Fix issue related to decoding post request raized an exception due to a split of information by chunk not correctly taken into account by the decoder

Motivation:

If the last item analyzed in a previous received HttpChunk/HttpContent was a part of an attribute's name, the read index was not set to the new right place and therefore raizing an exception in some case (since the "new" name analyzed is empty, which is not allowed so the exception).

What appears there is that the read index should be reset to the last valid position encountered whatever the case. Currently it was set when only when there is an attribute not already finished (name is ok, but content is possibly not).

Therefore the issue is that elements could be rescanned multiple times (including completed elements) and moreover some bad decoding can occur such as when in a middle of an attribute's name.

Modifications:

To fix this issue, since "firstpos" contains the last "valid" read index of the decoding (when finding a '&', '=', 'CR/LF'), we should add the setting of the read index for the following cases:

'lastchunk' encountered, therefore finishing the current buffer
any other cases than current attribute is not finished (name not found yet in particular)
So adding for this 2 cases:

undecodedChunk.readerIndex(firstpos);

Result:

Now the decoding is done once, content is added from chunk/content to chunk/content, name is decoded correctly even if in the middle of 2 chunks/contents.
A Junit test code was added: testChunkCorrect that should not raized any exception.
[#2262] Fix NPE triggered by unresolveable InetSocketAddress in epoll transport

Motivation:
At the moment when an unresolvable InetSocketAddress is passed into the epoll transport a NPE is thrown

Modifications:
Add check in place which will throw an UnknownHostException if an InetSocketAddress could not been resolved.

Result:
Proper handling of unresolvable InetSocketAddresses
[#2323] Make it clear a Channel must be closed to release all resources

Motivation:
Ensure the user know the Channel must be closed to release resources like filehandles.

Modifications:
Add some extra javadoc.

Result:
More clear documentation
[#2326] Add constructor to NioServerSocketChannel which accepts a ServerSocketChannel

Motivation:
Allow the user to create a NioServerSocketChannel from an existing ServerSocketChannel.

Modifications:
Add an extra constructor

Result:
Now the user is be able to create a NioServerSocketChannel from an existing ServerSocketChannel, like he can do with all the other Nio*Channel implemntations.
Replace usage of UnknownHostException with UnresolveableAddressException. Part of [#2262]

Motivation:
We better use UnresolveableAddressException as NIO does the same.

Modifications:
Replace usage of UnknownHostException with UnresolveableAddressException

Result:
epoll transport and nio transport behave the same way
Set timeout for SocketSslEchoTest

Motivation:

We are seeing EpollSocketSslEchoTest does not finish itself while its I/O thread is busy.  Jenkins should have terminated them when the global build timeout reaches, but Jenkins seems to fail to do so.  What's more interesting is that Jenkins will start another job before the EpollSocketSslEchoTest is terminated, and Linux starts to oom-kill them, impacting the uptime of the CI service.

Modifications:

- Set timeout for all test cases in SocketSslEchoTest so that all SSL tests terminate themselves when they take too long.
- Fix a bug where the epoll testsuite uses non-daemon threads which can potentially prevent JVM from quitting.
- (Cleanup) Separate boss group and worker group just like we do for NIO/OIO transport testsuite.

Result:

Potentially more stable CI machine.
Fix 'incompatible event loop' regression

Motivation:

Previous commit (2de65e25e90dec5c0a28b2d57e6c6d15d5a49087) introduced a regression that makes the epoll testsuite fail with an 'incompatible event loop' error.

Modifications:

Use the correct event loop type.

Result:

Build doesn't fail anymore.
Perform cross-tests between NIO and epoll transport

Motivation:

The epoll testsuite tests the epoll transport only against itself (i.e. epoll x epoll only).  We should test the epoll transport also against the well-tested NIO transport, too.

Modifications:

- Make SocketTestPermutation extensible and reusable so that the epoll testsuite can take advantage of it.
- Rename EpollTestUtils to EpollSocketTestPermutation and make it extend SocketTestPermutation.
- Overall clean-up of SocketTestPermutation
  - Use Arrays.asList() for simplicity
  - Add combo() method to remove code duplication

Result:

The epoll transport is now also tested against the NIO transport.  SocketTestPermutation got cleaner.
Add -verbose:gc option for test runs

Motivation:

While investigating the recent CI machine crashes, I observed that the
JVM processes spawned by surefire sometimes take up to 1 GiB RAM.
Consuming large amount of memory isn't really a problem, but we need to
make sure no GC trashing is occuring during the tests.

Modifications:

Add -verbose:gc option to the test JVM arguments

Result:

We can determine if there is any GC anomalies going on in our CI
machine.