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>
YUM: Add options to enable and disable Yum plugins

Adds two options you can define:
* disabled_plugins: A comma-separated list of plugins to disable
* enabled_plugins: A comma-separated list of plugins to enable

This allows you to run bcfg2 with certain plugins enabled or disabled
when they're not set that way in the yum configuration.  This is
useful because the Bcfg2 YUM plugin is initialized before it can read
in any files that might overwrite yum plugin configuration.
Merge pull request #215 from jsbillings/yum-plugin

YUM: Add options to enable and disable Yum plugins
Merge branch 'ssl-protocol-fix' of github.com:solj/bcfg2 into maint