Acceptance volume cmp 967

Fixes https://clusterhq.atlassian.net/browse/FLOC-967
The previous code constructed a dictionary representing the current deployment, and compared it with `assertEqual` to the given dictionary. This worked well.

The current code uses multiple assertions - one for each node in the given `expected_deployment`. This means that the test failure only shows you what is wrong with one node. It doesn't, like the old code, show you the whole state you want to compare. There is less debugging information here. For example, the old code would show you that you expected MongoDB on `node_1` but actually it is `node_2`, while this code will show you just that you expected MongoDB on `node_1` but it isn't there.