crtools: initial skeleton for cr_service

The criu service is a daemon, that opens a unix socket and listens for
incoming requests. The requests will be declared in protobuf/rpc.proto
and for now will only contain the 'dump' request.

Signed-off-by: Ruslan Kuprieiev <kupruser@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>