multiple frontend mode: avoid unnecesary slurmd configuration warning

When running in multiple-slurmd mode, the actual hardware configuration reported
by the slurmd is ignored, and internal entries (via register_front_ends() just
use 1 as dummy value for CPUs, sockets, cores, and threads.

On a dual-core service node this lead to continual warning messages like

[2011-04-01T10:06:40] Node configuration differs from hardware
   Procs=1:2(hw) Sockets=1:1(hw)
   CoresPerSocket=1:2(hw) ThreadsPerCore=1:1(hw)
[2011-04-01T10:07:24] Node configuration differs from hardware
   Procs=1:2(hw) Sockets=1:1(hw)
   CoresPerSocket=1:2(hw) ThreadsPerCore=1:1(hw)

Since validate_nodes_via_front_end() ignores the reported values, it is safe
to use the actual hardware configuration here, which also helps with taking
stock of the current cluster configuration (e.g. via scontrol show slurmd).

After applying this patch, the slurmds report without warnings as

[2011-04-01T12:03:38] slurmd version 2.3.0-pre4 started
[2011-04-01T12:03:38] slurmd started on Fri 01 Apr 2011 12:03:38 +0200
[2011-04-01T12:03:38] Procs=2 Sockets=1 Cores=2 Threads=1 Memory=3886 TmpDisk=1943 Uptime=14355