Proxy.py: Pass through SSL protocol option

Previously we were not passing through the SSL protocol specified in the
client's bcfg2.conf which caused it to unconditionally be set to
xmlrpc/ssl. While this appears to automagically work with newer versions
of openssl, the version in e.g. centos5 will fail if the server is set
to use TLSv1.

This commit passes through the setting from the client's bcfg2.conf so
that older clients can talk to servers which are set to TLSv1 (in order
to mitigate the effects of POODLE).

Signed-off-by: Sol Jerome <sol.jerome@gmail.com>
What happens if protocol isn't sent to this method and it defaults to None? It looks like the `connect` method of SSLHTTPConnection will bail out.