Document and assert support for TLS-PSK cipher suites.

This CL updates the Javadoc of SSLSocket and SSLEngine to list the
now supported TLS-PSK cipher suites. It also adds tests to assert
that these cipher suites are actually supported by SSLSocket and
SSLEngine.

Bug: 15073623
Change-Id: I8e59264455f980f23a5e66099c27b5b4d932b9bb
7 files changed