[pmix server] Simplify usock_peer_recv_blocking, removing pmix server specific
operations.
[pmix server] Introduce a set of routines for pmix_server_peers
incapsulation. Will be intensively used in next commits.
[pmix server] Simplify usock_peer_recv_blocking, removing pmix server specific
operations.
[pmix server] Cleanups to the previous commit. Quick runtime test - OK.
[pmix server] Cleanup connection_handler. Now peer transits directly to
CONNECTED state or get dropped. No intermediate stages are needed.
[pmix server] Cleanup pmix_server_send_connect_ack and
usock_peer_send_blocking.
[pmix server] Remove duplicated and unneeded functions.