Basic library for parsing TLS/SSL ClientHellos in tests.

CTS tests in libcore assert certain properties of TLS/SSL and HTTPS
stacks, but they do not check whether these are correctly reflected
in the underlying TLS/SSL traffic generated by these stacks.

This basic TLS wire-protocol library will enable CTS tests to inspect
in detail ClientHello messages, such as which protocol is being
signalled as the higest supported by the client, which cipher suites
are enabled, whether SNI extension is provided and set to the correct
value.

As an example, in this CL I switched one test in SSLSocketTest to
this library.

Change-Id: I93251dd873a78ec7f6caa704b71f5fa0ecf2c2f2