gwcelery detchar checkvectors reporting a bad state and malformed JSON reports

It appears that the detchar checkvectors process is reporting "unknown" states to the DQR, which it is not allowed (see the DQR docs). The closest allowed state is probably "error", but perhaps "human input needed" could also serve.

gwcelery has posted DQR reports for 15 superevents (starting on Oct 26, 2018) and has returned a bad state for all of them. The DQR diagnostic tools yields

>> dqr-stats -v --superevents --gracedb-url https://gracedb-playground.ligo.org/api/ "$(lalapps_tconvert 26 Oct 2018) .. $(lalapps_tconvert)"
querying https://gracedb-playground.ligo.org/api/ for events with: 1224547218 .. 1225127909
found 15 events
...
summarizing TASK: "gwcelery detchar checkvectors" performance
TASK: "gwcelery detchar checkvectors" latency until complete
      quantile | latency (sec)
         0.900 | 18.000
TASK: "gwcelery detchar checkvectors" state
          pass |  fail | human_input_needed | missing | error | bad_state | empty
count :      0 |     0 |                  0 |       0 |     0 |        15 |     0
 frac :  0.000 | 0.000 |              0.000 |   0.000 | 0.000 |     1.000 | 0.000

Furthermore, the detchar process is returning malformed JSON reports; the list of links is not properly formatted, see the report for S181101b. Looking at the source code, I really do not understand how this is happening. But somehow the JSON reports a list containing a list of objects instead of just the list of objects, as it's supposed to (again, see the DQR docs).

It also looks like the summary message is not properly formatted, it drops some content based on the replacement occurring in this line (only 2 {} instead of 3).

/cc @geoffrey.mo @erik-katsavounidis