Option to dedicate nodes to single user

Add the ability for a compute node to be allocated to multiple jobs, but
restricted to a single user. Added "--exclusive=user" option to salloc,
sbatch and srun commands. Added "owner" field to node record, visible using
the scontrol and sview commands. Added new partition configuration parameter
"ExclusiveUser=yes|no".  Add "Shared=user" job state information.