Added ModifyImageAttribute
Added test case for ModifyImageAttribute
Merge pull request #6 from jmassara/ami_image_attrs

ec2: added ModifyImageAttribute
Simplify ModifyImageAttributes

/cc @jmassara - I think this is much simpler. Thoughts?
ec2: more comprehensive ModifyImageAttribute test
ec2: use HTTP proxy from env vars if available
ec2: Added CopyImage API call
Merge pull request #7 from jmassara/copyimage

ec2: Added CopyImage API call
ec2: Added tagSet to Image type
Merge pull request #8 from jmassara/tagSet

ec2: Added tagSet to Image type
ec2: Fixed Image type to use Tag
Merge pull request #9 from jmassara/tagSet

ec2: Fixed Image type to use Tag
ec2: Support NoDevice block mapping