Seems that somebody repaired devices earlier today.  So, now the
fix is easy:

$ balance_pool -t 6 bvt daisy_spring
daisy_spring bvt pool: Target of 6 is above minimum.

Balancing ['model:daisy_spring'] bvt pool:
Total 5 DUTs, 4 working, 1 broken, 0 reserved.
Target is 6 working DUTs; grow pool by 2 DUTs.
['model:daisy_spring'] suites pool has 4 spares available for balancing pool bvt
['model:daisy_spring'] bvt pool will return 1 broken DUTs, leaving 0 still in the pool.
Transferring 1 DUTs from bvt to suites.
Updating host: chromeos6-row2-rack16-host16.
Removing labels ['pool:bvt'] from host chromeos6-row2-rack16-host16
Adding labels ['pool:suites'] to host chromeos6-row2-rack16-host16
Transferring 2 DUTs from suites to bvt.
Updating host: chromeos6-row2-rack16-host2.
Removing labels ['pool:suites'] from host chromeos6-row2-rack16-host2
Adding labels ['pool:bvt'] to host chromeos6-row2-rack16-host2
Updating host: chromeos6-row2-rack16-host18.
Removing labels ['pool:suites'] from host chromeos6-row2-rack16-host18
Adding labels ['pool:bvt'] to host chromeos6-row2-rack16-host18