[pmix server] pmix_server cleanups:
1. Move pmix_server_start_listening  since this is connection-related
tool. Remove event manipulation part from there.
2. Fix bugs in peer hash table traversal.
[Compile OK, Runtime -]
[pmix server] Fix output in pmix_server_start_listening.
[pmix server] Move all peer message processing to the
pmix_peer_process.c file.
[Compile - OK, Runtime -]