New improvements in ec2 and cloudstack driver:

1. Added new functionality for ec2:

* list_volumes
* list_snapshots
* destroy_volume_snapshot
* create_volume_snapshot
* delete_keypair
* ex_destroy_image
* ex_modify_image_attributes

2. CloudStack changes

* add possibilities create a port range rules in PortForwardingRule
* fix some methods names (list keypairs)I

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
Some pep8, style and docstring fixes.
Update CHANGES.