Implement a pre-pass-version of agent-rank-setting

which contacts the agent server, so that it can create the mapping
between the jobid, vpid and the desired rank/vpid (since the vpid
actually gets used as the rank) before the actual assignment takes
place. This is necessary because the assignment must be in ascending
order since it writes into an array of process-pointers of the current
group which will cause problems if the first (0th) field in the array
has not yet been initialized but another (already initialized) process
wants to contact it.