Provide authentication mechanisms for Hermes

For maintaining security guarantees, we can make it so that each process connects to the runtime using a POSIX domain socket. We can obtain process credentials (user, group, etc) and store in a table.

We can then create either per-process or per-user queues (per-user would possibly save some memory, but would have the potential for faulty processes to spread their malice to non-faulty processes by corrupting a queue). We could also implement grouped process queues for MPI-based programs, where each process in a group shares a queue.

This way there are privilege guarantees regarding how programs can interact with the Hermes runtime.