Failure to create a space should be a warning, not an error in "assemble"

It turns out that creating a space in Cloud Foundry (including Bluemix) requires a fairly high level of permission. Not all users of `kale` with have enough privilege to create a space.

Currently, "assemble" will fail if it cannot create a space. This is unhelpful for users who are not able to create a space in the organization they want to be creating services in.
