Reduce data loaded before loading tests

[timifasubaa]

This PR pushes down the CI build times for python tests by reducing the tables loaded before running the tests.

@john-bodley @mistercrunch @michellethomas

[codecov-io]

Codecov Report

Merging #6298 into master will decrease coverage by 3.93%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #6298      +/-   ##
==========================================
- Coverage   77.31%   73.38%   -3.94%     
==========================================
  Files          67       67              
  Lines        9581     9582       +1     
==========================================
- Hits         7408     7032     -376     
- Misses       2173     2550     +377

Impacted Files	Coverage Δ
superset/cli.py	35.43% <0%> (-0.15%)	⬇️
superset/data/deck.py	11.29% <0%> (-87.1%)	⬇️
superset/data/flights.py	25.8% <0%> (-74.2%)	⬇️
superset/data/misc_dashboard.py	27.27% <0%> (-72.73%)	⬇️
superset/data/country_map.py	27.58% <0%> (-72.42%)	⬇️
superset/data/random_time_series.py	28.57% <0%> (-71.43%)	⬇️
superset/data/long_lat.py	29.72% <0%> (-70.28%)	⬇️
superset/data/multiformat_time_series.py	21.62% <0%> (-67.57%)	⬇️
superset/data/bart_lines.py	38.46% <0%> (-61.54%)	⬇️
superset/data/sf_population_polygons.py	39.13% <0%> (-60.87%)	⬇️
... and 6 more

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[mistercrunch]

Ballpark before/after times?

[timifasubaa]

@mistercrunch Shaved off about ~ 1 minute from the Python tests. From 5-6 mutes to 4 minutes

[michellethomas]

Not sure how others feel about removing the loading of these data sets completely. I wonder if we can have a flag for loading all data vs loading basic data sets. That way if some tests want to use all data they can.

[timifasubaa]

@michellethomas Agree. I updated the PR to only remove it completely from the tests loading.
The superset load_examples command will continue to load all the data but when the -t flag or equivalent is added, it will add only the subset that's used in the tests.

[timifasubaa]

PING

[mistercrunch]

@michellethomas superset load_examples still loads everything, people can add more datasets to load if they want to testing purposes. LGTM if @michellethomas is cool with it

[michellethomas]

This is nested under if not load_test_data:

[timifasubaa]

Done

[michellethomas]

lgtm