databases/py-riak: Update to 2.1.0rc1

• Update to 2.1.0rc1
• Add py-openssl to RUN_DEPENDS
• Add LICENSE_FILE
• Update COMMENT (from setup.py)
• Modernise Python framework entries
• Limit Python version to -2.7 (As recommended upstream)

Announcement:

http://lists.basho.com/pipermail/riak-users_lists.basho.com/2014-July/015631.html

PR: 189917