Updated EMR to use SigV4 and AWS JSON protocol.
API updates for Amazon Redshift.

Adds cluster snapshot identifiers to CopyClusterSnapshot and
DeleteClusterSnapshot. Enables better status reporting for
restoring from snapshots.
Update AWS::SNS::Client API to latest version.

SNS now supports mobile push.
Fix EMR spec stubbing.

JSON stubbing is not as sophisticated as XML stubbing, added missing
values to spec tests.
Bump version to 1.15.0