RFR: 7903543: Making Agent's connections more NIO friendly

[Dmitry Bessonov]

This is for refactoring few JT agent's helper classes to support and work with SocketChannels

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Commit messages:
 - minor cleanups
 - minor cleanups
 - 7903543: Making Agent's connections more NIO friendly

Changes: https://git.openjdk.org/jtharness/pull/51/files
 Webrev: https://webrevs.openjdk.org/?repo=jtharness&pr=51&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903543
  Stats: 166 lines in 8 files changed: 66 ins; 10 del; 90 mod
  Patch: https://git.openjdk.org/jtharness/pull/51.diff
  Fetch: git fetch https://git.openjdk.org/jtharness.git pull/51/head:pull/51

PR: https://git.openjdk.org/jtharness/pull/51