Add support for multiple encryption methods

We use only one encrypt() method but it returns the method to decrypt
the data. This way we can change the encryption mechanism but
always have a way to know how to decrypt whatever is stored.

Change-Id: I2315a33105a8766f69d02f0617af39a9dae19ddf
Partial-bug: #1251647
Add a schema for the AWS::EC2::Instance Volumes property

Change-Id: I1d2e6854d0fe81d5d0b9272f65502d71a39ad511
Use property name constants in CinderVolume

blueprint property-schema-conversion

Change-Id: I38719a21ec89bbc8b74f57184a83a92c1cfb7dda
Merge "Add a schema for the AWS::EC2::Instance Volumes property"
Merge "Use property name constants in CinderVolume"
Merge "Add support for multiple encryption methods"