Add support to explicitly set the enabled SSL protocols

For some reason when the server uses SSLv3 the lib is not able to decode
the messages properly. To workaround this issue it's needed to set the
enabled protocols to SSLv3 (only).

This patch enables to explicitly set the enabled protocols.

For more info: https://github.com/koush/AndroidAsync/issues/174
Merge pull request #176 from luisgabriel/master

Add support to explicitly set the enabled SSL protocols
Merge in upstream/master, and redo configurator API to support multiple AsyncSSLEngineConfigurators.