cloudstack-4308 Add API listCapabilities for KVMSnapshotEnabled so that UI can use it for recurring snapshot.

Conflicts:
	api/src/org/apache/cloudstack/api/command/user/config/ListCapabilitiesCmd.java
	api/src/org/apache/cloudstack/api/response/CapabilitiesResponse.java
	server/src/com/cloud/server/ManagementServerImpl.java
CLOUDSTACK-669: put system vm work under new vmsync model
CLOUDSTACK-5354: UI > update ISO > make isExtractable, isFeatured checkbox non-editable to normal user.