Fixed inheritance hierarchy for Swift and Cloud Files to avoid problems when using BlobStore.

This fixes problems like 

    java.lang.IllegalArgumentException: backend type: org.jclouds.rest.RestContext<org.jclouds.cloudfiles.CloudFilesClient, org.jclouds.cloudfiles.CloudFilesAsyncClient> not assignable from org.jclouds.rest.RestContext<? extends org.jclouds.openstack.swift.SwiftClient, ? extends org.jclouds.openstack.swift.SwiftAsyncClient>

when trying to use the BlobStore with Swift/Cloud Files.