Removing race conditions from acceptance tests

By default, `go test` will execute multiple builds in parallel - meaning that tests across multiple packages are run asynchronously. This is fine for unit tests because they're fully isolated against other packages, but this is not the case for our acceptance tests. 

This explains why we're running into a lot of weird API responses when provisioning servers, as described in #241. This is probably because Neutron is creating networks _at the same time_ as Compute tests are provisioning servers. You can disable this parallelization with the [p flag](https://golang.org/cmd/go/#hdr-Compile_packages_and_dependencies).