Add more burst buffer state info reporting
Rename burst_buffer/none to burst_buffer/generic
Improve config preservation on reconfig

The logic was flawed to preserve BurstBufferType on slurmctld reconfig
In addition for many plugins, one could go from no value to some
value (i.e. a change in plugin) without reconfiguring. In this case,
the slurmctld logic would not match what is in slurm.conf or reported
by "scontrol show config".
burst_buffer: support more variety in size specs

MB, GB, TB, PB, or N (for nodes).
Also added a BB_SIZE_IN_NODES flag to slurm.conf