fix: nvd3 bar chart sortby metric

[zhaoyongjie]

SUMMARY

currently, nvd3 bar chart(non-timeseries) can not be sorted by metric. this PR fixed it.

closes: #15260

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

before

issue link: #15260

after

Jun-23-2021.02-34-07.mp4

TESTING INSTRUCTIONS

tested in local

ADDITIONAL INFORMATION

• Has associated issue: [chart]Bar Chart sorting does not appear to work as intended. #15260
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[zhaoyongjie]

For the distributed bar only a single metric can be sorted.

[codecov]

Codecov Report

Merging #15318 (da4d734) into master (ab153e6) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #15318      +/-   ##
==========================================
+ Coverage   77.14%   77.22%   +0.08%     
==========================================
  Files         973      973              
  Lines       50473    50481       +8     
  Branches     6183     6183              
==========================================
+ Hits        38938    38985      +47     
+ Misses      11329    11290      -39     
  Partials      206      206              

Flag	Coverage Δ
hive	81.41% <100.00%> (-0.01%)	⬇️
mysql	81.68% <100.00%> (-0.01%)	⬇️
postgres	81.69% <100.00%> (-0.01%)	⬇️
presto	81.40% <100.00%> (?)
python	82.23% <100.00%> (+0.15%)	⬆️
sqlite	81.33% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/viz.py	56.52% <100.00%> (+0.04%)	⬆️
superset/views/core.py	75.54% <0.00%> (-0.04%)	⬇️
superset/views/sql_lab.py	60.68% <0.00%> (ø)
superset/models/core.py	90.02% <0.00%> (+0.26%)	⬆️
superset/connectors/sqla/models.py	89.87% <0.00%> (+1.41%)	⬆️
superset/db_engine_specs/presto.py	90.31% <0.00%> (+5.89%)	⬆️

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[villebro]

LGTM - based on the code changes it appears sorting didn't support adhoc metrics before, thanks for fixing both issues :)