[JENKINS-25218] - Hardening of FifoBuffer operation logic

[oleg-nenashev]

It is a version of #100 submitted against the master branch

The most of JENKINS-25218 has been handled in 3ea38c8 by @andresrc. But there are still potential issues in the FifoBuffer behavior.

Changes:

• - Add closedRequested and handle it in multiple threads, which used to prevent close() calls previously
• Fix potential NPE in FifoBuffer receiver
• Do not rely on external code when we receive ClosedChannelException from the underlying channel

[oleg-nenashev]

#100 has been berged, this guy is not required anymore