LIBCLOUD-377: Adding extra attribute to NodeImage

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
Modify EC2 driver create_node method and make extension argument for assigning
a node to a security group consistent with the OpenStack implementation.

Previously the argument was called ex_securitygroup, now it's called
ex_security_groups.

Part of LIBCLOUD-375.
docs: Add new "Working with the object oriented APIs" chapter.
LIBCLOUD-379: Adding CloudStack examples to docs

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
LIBCLOUD-380: Add import_keypair functions and tests

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
Update changes.
Fix Python 2.5 compatibility issue.
Add support for floating IPs to OpenStack