correctly set alloc state of node in select/linear

fix of the following problem:
if a node is excised from a job and a reconfiguration(e.g., update
partition) is done when the job is still running, the node will be left
in state idle but not available any more until the next
reconfiguration/restart of slurmctld after the job finished.
Merge branch 'slurm-2.5'