Fix vector-scalar comparisons

[owen-d]

• formats shards in downstreamers for better logging
• Make vector-scalar comparisons filter by default, but not set the results to 0 or 1.

$ logcli query 'sum(rate({filename=~"/var/log/wifi.*"}[1m])) > 1'
http://localhost:3100/loki/api/v1/query_range?direction=BACKWARD&end=1591386888234918000&limit=30&query=sum%28rate%28%7Bfilename%3D~%22%2Fvar%2Flog%2Fwifi.%2A%22%7D%5B1m%5D%29%29+%3E+1&start=1591383288234918000
[
  {
    "metric": {

    },
    "values": [
      [
        1591384744.234,
        "1893.2666666666664"
      ],
      [
        1591384758.234,
        "1893.2666666666664"
      ],
      [
        1591384772.234,
        "1893.2666666666664"
      ],
      [
        1591384786.234,
        "1893.2666666666664"
      ],
      [
        1591384800.234,
        "1074.3166666666666"
      ]
    ]
  }
]

vs

$ logcli query 'sum(rate({filename=~"/var/log/wifi.*"}[1m])) > bool 1'
http://localhost:3100/loki/api/v1/query_range?direction=BACKWARD&end=1591386974813316000&limit=30&query=sum%28rate%28%7Bfilename%3D~%22%2Fvar%2Flog%2Fwifi.%2A%22%7D%5B1m%5D%29%29+%3E+bool+1&start=1591383374813316000
[
  {
    "metric": {

    },
    "values": [
      [
        1591384746.813,
        "1"
      ],
      [
        1591384760.813,
        "1"
      ],
      [
        1591384774.813,
        "1"
      ],
      [
        1591384788.813,
        "1"
      ]
    ]
  }
]

[cyriltovena]

LGTM

[codecov-commenter]

Codecov Report

Merging #2189 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2189      +/-   ##
==========================================
- Coverage   61.97%   61.96%   -0.02%     
==========================================
  Files         154      154              
  Lines       12432    12432              
==========================================
- Hits         7705     7703       -2     
- Misses       4120     4121       +1     
- Partials      607      608       +1     

Impacted Files	Coverage Δ
pkg/logql/evaluator.go	92.72% <100.00%> (+0.41%)	⬆️
pkg/querier/queryrange/downstreamer.go	95.87% <100.00%> (ø)
pkg/promtail/targets/tailer.go	76.13% <0.00%> (-2.28%)	⬇️
pkg/ingester/transfer.go	65.49% <0.00%> (-1.41%)	⬇️