Benchmark multiple volumes
Cleanup code
Compatibility for Python 3

dict_values objects don't support indexing (since they're views)
Force time based benchmarks (no size)
Fix mishandling of errors in API client

In the unusual case that we don't get an error dict (that is, the API
itself messed up), we shouldn't die with an AttributeError, and raise
an APIError instead.
Merge pull request #1 from Scalr/multi-volumes

Benchmark multiple volumes