RFR: JDK-8282686: Add constructors taking a cause to SocketException

[Joe Darcy]

Please review this small API enhancement to add the usual constructors taking a cause to SocketException and then update uses of initiCause on creating SocketException to instead pass the cause via the constructor.

Please also review the CSR: https://bugs.openjdk.java.net/browse/JDK-8282688

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Commit messages:
 - JDK-8282686: Add constructors take a cause to SocketException

Changes: https://git.openjdk.java.net/jdk/pull/7705/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7705&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282686
  Stats: 48 lines in 6 files changed: 23 ins; 12 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7705.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7705/head:pull/7705

PR: https://git.openjdk.java.net/jdk/pull/7705