Only change default network settings on Rackspace Cloud

Having this package installed makes it very frustrating to use the nova
cli with other cloud providers, because some default network settings
are set that don't make sense anywhere but the Rackspace Cloud. This
patch adds a simple check to see if the client is actually being used
against the Rackspace Cloud.
Merge pull request #8 from gtmanfred/master

use add_arg from novaclient again
Merge pull request #9 from gtmanfred/master

use default args if no args are passed
Merge pull request #7 from sorenh/master

Only change default network settings on Rackspace Cloud
Update version and URL
sometimes this variable is not set

When using bypass_url, and supplying a token.