[rhc54]

#2877 gave a DVM's controller and daemons an ID of their own making and passed it to PMIx_server_init as PMIX_SESSION_ID, because PMIx named a session server's rendezvous file by that attribute. But PMIX_SESSION_ID is the session's ID as the scheduler assigned it, and clients and tools read it as such. The DVM's computed value doesn't belong there.

openpmix/openpmix#4385 adds PMIX_SESSION_RNDZ_ID, which only names the rendezvous file, and falls back to PMIX_SESSION_ID when it isn't given.

Change

• Pass the computed ID as PMIX_SESSION_RNDZ_ID when the PMIx defines it, and nothing as PMIX_SESSION_ID. A PMIx without the attribute names no session server's file by an ID, so there is nothing to pass.

• Rename what prted: name the session a DVM is the session server of #2877 added to match:

  • the MCA parameter pmix_session_id is now pmix_session_rndz_id;
  • prte_pmix_server_compute_session_id() is now prte_pmix_server_compute_rndz_id().

  Neither has been in a release.

This PR and openpmix/openpmix#4385 can merge in either order. Against PMIx master as it is now, PRRTE builds and passes nothing. Against #4385 before this PR, the fallback names the file by the PMIX_SESSION_ID that #2877 passes.

Testing

• Unit tests: pass, including the renamed ID checks.
• Built against PMIx master (without the attribute): builds clean.
• Built against ptl: a session-level server is named by a rendezvous ID openpmix#4385:
  • the debugger examples pass;
  • two DVMs of one user on a node and a prterun beside them all start, each DVM's file is named by its own ID, --pid reaches either DVM, and prun with no target lists both;
  • the docker swarm with PMIX_SRC set to that branch: 936 passed, 0 failed, 3 skipped.