Refactor cinder volume v2 API changes

The handling of name and description for v2 API is duplicated for
handle_create and handle_update methods. This patch defines a new
method which handles the differences in parameter names thereby
avoiding duplication and keeping the changes restricted to this
method to the extent possible.

Change-Id: I891aeea3fe5d7cb22be27e05ab72857af668e4ed
Add is_conflict() to client plugins

Change-Id: I0f4239869da8cab505723ff6b2dfbb37bef83ff1
Add a handle_delete method to SwiftSignalHandle

Swift containers and objects that were created by a particular
SwiftSignalHandle should be deleted when the resource is deleted.

Change-Id: Id9df03e139ca0632996f4f66c5f39e27bb04d1fb
Closes-Bug: #1379040
Merge "Refactor cinder volume v2 API changes"
Merge "Add is_conflict() to client plugins"
Merge "Add a handle_delete method to SwiftSignalHandle"