[openstack|compute] authenticate_v2 fixes

* Add connection_options to Fog::Connection when
authenticating so we can disable SSL cert verification for example.
* Do not use hardcoded keystone 5000 port

Sample code:

    conn = Fog::Compute.new({
      :provider => 'OpenStack',
      :openstack_api_key => "changeme",
      :openstack_username => "user@bvox.net",
      :openstack_auth_url => "https://auth-server/v2.0/tokens",
      :connection_options => { :ssl_verify_peer => false }
    })

lib/fog/openstack.rb

@@ -107,7 +107,7 @@ module Fog
       unless svc
         unless @openstack_tenant
           response = Fog::Connection.new(
-            "#{uri.scheme}://#{uri.host}:5000/v2.0/tenants", false).request({
+            "#{uri.scheme}://#{uri.host}:#{uri.port}/v2.0/tenants", false, connection_options).request({
             :expects => [200, 204],
             :headers => {'Content-Type' => 'application/json',
                          'X-Auth-Token' => body['access']['token']['id']},