refactor subscription call which has many method parameters.

Introduce a class SubscriptionData calss which holds the data such as cartridgetype, repoURL..... SO we don't need to send all
the paramertes to method calls, just send the SubscriptionData object
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-stratos
removing snapshotID from persistance mapping and adding persistanceRequired boolean value
Adding persistance mapping when subscribing for a cartridge
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-stratos
adding a comment in nodes.pp
Fixed list-subscribed-cartridge command error in CLI
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-stratos
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-stratos