Patch to add storage volume management to the libcloud.compute.base module, as well as completing the CloudStack implementation and an initial implementation for EC2

Awesome patch, thanks! I have merged into trunk with some minor changes:

• Removed trailing whitespace and fixed pep8 style issues (single blank line between methods in a class, no whitespace around = operator, is not None instead of != None, etc.)
• Minor cleanup in docstrings
• Added _volume suffix to all the StorageVolume related methods on the NodeDriver class (for API consistency)
• Changed ex_describe_tags in EC2 driver so it's consistent ex_create_tags and ex_delete_tags

This is a big step forward but I think that we are missing a list_volumes() method. It is important to me and seems inconsistent that LinCloud has create and delete methods for storage volumes without at way to find out what has been created.

I would like to propose a new method to the NodeDriver class consistent with list_nodes() and similar methods to do this. Here it is:

def list_volumes(self):
"""
List storage volumes.
@return: C

of L

objects
"""
raise NotImplementedError(
'list_volumes not implemented for this driver')

list_volumes sounds reasonable to me. Next step is checking if most of the providers support this functionality and implementing it.