Recent toImage problems

[etpinard]

Currently on master, ./tasks/noci_test.sh image outputs

exported mapbox_0, in 2223.43075 ms
exported mapbox_angles, in 1665.376115 ms
exported mapbox_bubbles, in 1178.323781 ms
exported mapbox_bubbles-text, in 1258.123461 ms
exported mapbox_carto-style, in 835.072415 ms
exported mapbox_choropleth0, in 995.291759 ms
export error 525 for mapbox_choropleth0-legend - plotly.js error
  {"type":"error"}
exported mapbox_choropleth-multiple, in 1718.333484 ms
exported mapbox_choropleth-raw-geojson, in 1662.899144 ms
exported mapbox_connectgaps, in 1533.387381 ms
exported mapbox_custom-style, in 1875.924 ms
exported mapbox_density0, in 1156.254864 ms
export error 525 for mapbox_density0-legend - plotly.js error
  {"type":"error"}
exported mapbox_density-mulitple, in 1433.619021 ms
export error 525 for mapbox_density-mulitple_legend - plotly.js error
  {"type":"error"}
exported mapbox_earthquake-density, in 1440.466529 ms
exported mapbox_fill, in 1072.05885 ms
exported mapbox_geojson-attributes, in 2012.565512 ms
exported mapbox_layers, in 2141.55931 ms
exported mapbox_osm-style, in 834.893128 ms
exported mapbox_stamen-style, in 894.038581 ms
exported mapbox_symbol-text, in 1134.548921 ms
exported mapbox_texttemplate, in 1025.165576 ms
exported mapbox_white-bg-style, in 696.264266 ms

where the mapbox mocks added in #4386 fail to export using orca.

These problematic mocks also fail to export via Plotly.toImage and Plotly.downloadImage in the test-dashboard console.

---

I suspect this problem is similar to #2914 and #1694

[etpinard]

While attempting to fix this bug, we should test orca image-exports for all the mocks added in #4386