Rename RDMA structures to make destination clear

Rename RDMA structures to make destination clear

RDMA has two data types that are named confusingly;
   RDMALocalBlock (pointed to indirectly by local_ram_blocks)
   RDMARemoteBlock (pointed to by block in RDMAContext)

RDMALocalBlocks, as the name suggests is a data strucuture that
represents the RDMAable RAM Blocks on the current side of the migration
whichever that is.

RDMARemoteBlocks is always the shape of the RAMBlocks on the
destination, even on the destination.

Rename:
     RDMARemoteBlock -> RDMADestBlock
     context->'block' -> context->dest_blocks

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Michael R. Hines <mrhines@us.ibm.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>