in the tightly coupled functions slurmd:stepd_completion and
slurmstepd:_handle_completion, a jobacct structure is
send from the main daemon to the step daemon to provide
the statistics of the children slurmstepd and do the aggregation.

The methodology used to send the structure is the use of
jobacct_gather_g_{setinfo,getinfo} over a pipe (JOBACCT_DATA_PIPE).
As {setinfo,getinfo} use a common internal lock and reading
or writing to a pipe is equivalent to holding a lock, slurmd and
slurmstepd have to avoid using both setinfo and getinfo over a
pipe or deadlock situations can occured. For example :
slurmd(lockforread,write)/slurmstepd(write,lockforread).

This patch remove the call to jobacct_gather_g_setinfo in slurmd
and the call to jobacct_gather_g_getinfo in slurmstepd ensuring
that slurmd only do getinfo operations over a pipe and slurmstepd
only do setinfo over a pipe. Instead jobacct_gather_g_{pack,unpack}
are used to marshall/unmarshall the data for transmission over the
pipe.
Patch by Matthieu Hautreux, CEA.

The patch committed here is a variation on the work by Matthieu.
Specifically, the logic is added to slurmstepd to read a new format
of RPC including an RPC version number and buffer with the data
structure. The slurmd however will not send the RPC in the new format
until SLURM version 2.5.