loom run import fails when re-used taskattempt present

[nhammond]

Encountered error even after flushing database. This comes up in the "sentece_scoring" demo, since there are two separate tasks scoring the letter "o".

from client:

loom run import sentence_scoring.yaml

...
  Skipping import because template already exists.
ERROR! Failed to import run: '(500) 500 Server Error: Internal Server Error for url: http://127.0.0.1:8000/api/runs/'

from server:

...
IntegrityError: (1062, "Duplicate entry 'e2969fd3-eb07-4adb-bf6f-3aa443a7e9f3' for key 'uuid'")
ERROR [2018-05-22 12:15:35,177] "POST /api/runs/ HTTP/1.1" 500 22676

e2969fd3-eb07-4adb-bf6f-3aa443a7e9f3 is a TaskAttempt with status "Finished", used by two separate tasks.

[nhammond]

Fixed in 83505d2