Update job's QOS before partition

This patch moves the QOS update of an existing job to be before the
partition update.  This ensures a new QOS value is the value used when
doing validations against things like a partition's AllowQOS and DenyQOS.

Currently if a two partitions have AllowQOS that do not share any QOS,
the order of updates prevents a job from being moved from one partition
to another using something like the following:

scontrol update job=<jobID> partition=<new part> qos=<new qos>