RFR: 8280494: (D)TLS signature schemes

[Xue-Lei Andrew Fan]

This update is to support signature schemes customization for individual (D)TLS connection.  Please review the CSR as well:
CSR: https://bugs.openjdk.java.net/browse/JDK-8280495
RFE: https://bugs.openjdk.java.net/browse/JDK-8280494

-------------

Commit messages:
 - 8280494: https://bugs.openjdk.java.net/browse/JDK-8280494
 - 8280494: Implementation: (D)TLS signature schemes

Changes: https://git.openjdk.java.net/jdk/pull/7252/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7252&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280494
  Stats: 297 lines in 4 files changed: 253 ins; 12 del; 32 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7252.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7252/head:pull/7252

PR: https://git.openjdk.java.net/jdk/pull/7252