Presubmit for run/markdown-preview/editor is consistently failing

[fhinkel]

https://source.cloud.google.com/results/invocations/32813175-423a-4ddf-9065-e7da9f31cea5/targets
https://source.cloud.google.com/results/invocations/e393577d-e306-4540-b4c9-141aea0747f4/targets

[grayside]

Note that a CL was submitted enabling Kokoro testing for a sample still in development. This will be fixed in #1752.

[grayside]

Not sure what priority this has, but adjusting the labels to indicate this bug only exists as a flag to indicate this test failure can be ignored.