Updates registry storage code to use this for better resumable writes.
Implements this interface for the following drivers:
+ Inmemory
+ Filesystem
+ S3
+ Azure
Signed-off-by: Brian Bland <brian.bland@docker.com>
Keeps old s3 driver, renames to s3goamz, registers new s3 driver as both
"s3" and "s3aws"
Changes cloudfront middleware to use aws-sdk-go
Signed-off-by: Brian Bland <brian.bland@docker.com>
