Reduce code duplication in import_image* methods
Signed-off-by: Joffrey F <joffrey@docker.com>

Refactor auth header computation

Add tasks methods and documentation.
Signed-off-by: Joffrey F <joffrey@docker.com>

Signed-off-by: Keerthan Reddy Mala <kmala@deis.com>

Stream helper has the ability to decode the responses from strings to
JSON. This commit enables this functionality on push and pull operations.
Signed-off-by: Aleksandar Topuzovic <aleksandar.topuzovic@gmail.com>

More relaxed version that matches the constraints imposed by the
current version of the docker daemon.
Few unit tests to verify the new cases.
Client.pull was trying to set the tag value when it wasn't supposed
to, fixed now.
utils.parse_repository_tag is simpler and supports @sha... notation
Signed-off-by: Joffrey F <joffrey@docker.com>

Add simpler version comparison functions
Add decorator to enforce minimum version in API methods
Fix utils imports
Add minimum_version decorators on API methods that needed it
GroupAdd test requires API version >= 1.20
Signed-off-by: Joffrey F <joffrey@docker.com>

Signed-off-by: Joffrey F <joffrey@docker.com>