Inconsistent uuid generation in azure_arm

## Summary

Azure returns inconsistent casing of the resource groups name in the id string, resulting in different uuid's for the same node (depending on what calls you make).

## Detailed Information

When a node is created, the resource groups name in the id string is lower case. In subsequent calls, like in list_nodes(), for some reason Azure returns the resource groups name in upper case. This results in a different uuid from when create_node() is called. This also breaks wait_until_running(). Forcing the id string to lower case in _to_node() seems to resolve this issue.

I made the change here: https://github.com/foospidy/libcloud/commit/2682d1229466fa577d4360ababd650d777ea49f3

I'd be happy to submit a PR.

Start by locating the Azure ARM provider's _to_node() method and compare how IDs are produced by create_node() and list_nodes(). Verify that resource-group casing no longer changes a node's UUID and that wait_until_running() works consistently; use the referenced commit as context and add or update focused tests if the provider's test structure identifies a suitable location.

Written by the indexing model from the issue text.