Add burst_buffer "teardown-fail" state

Add new burst buffer state of "teardown-fail" to indicate the burst buffer
    teardown operation is failing on specific buffers. This changes the numeric
    value of the BB_STATE_COMPLETE type. Any Slurm version 17.02 or 17.11 tool
    used to report burst buffer state information will report a state of "66"
    rather than "complete" for burst buffers which have been deleted, but still
    exist in the slurmctld daemon's tables (a very short-lived situation).
bug 4303