Allow RS LoadBalancer resource to have no nodes

It should be possible to create Rackspace load balancer with no nodes
now. There was an incidental bug in the way that the resource constructed
the node list that would prevent this.

Note that it won't be possible to actually use this to create a nodeless LB
until a new release of pyrax is made, but this change should be harmless enough
to be merged before that.

Change-Id: Icb9b50899cc13094e295280f89090def30cb4155
Closes-Bug: #1241221
Wrap engine exceptions in _()

Change-Id: Id68baa3542ec2804169a4411a9b6962a96487ec3
Partial-bug: #1199695
Prevent urlfetch from returning encoded chars

raw.read() is returning unprintable characters.  Iterate over the
decoded characters instead.

Closes-bug: #1240289

Change-Id: Ifa61dcc34286f2203407c657b5eb5ee2a099744d
Merge "Prevent urlfetch from returning encoded chars"
Merge "Allow RS LoadBalancer resource to have no nodes"
Merge "Wrap engine exceptions in _()"