Implemented action serialization, when operating on same computes (OMS-223)

I decided to implement it differently, than we initially devised. Instead of a marker interface, I've implemented a class-wide lock registry with Twisted deferred-aided action chaining/serialization. This allowed me to generalize the implementation over all of the Compute-specific actions (which I realized by extracting a base class called ComputeAction and renaming old ComputeAction into VComputeAction to better reflect its true purpose and context).