The image tests are now able to upload images to Azure and boot them there.
However, the documentation on how to set up the required resources in Azure
was missing. This commit adds it.
coveralls doesn't work from GitHub actions. Its "github" service type
uses the GITHUB_TOKEN from the action, which only has read access when
invoked from a forked repository.
codecov gets this right: it validates that an uploaded coverage file
originated from a GitHub action run by asking GitHub, and then uses its
OAuth credentials (through the Marketplace App) to comment and set
status.
Also, coveralls requires a third-party package to convert go's coverage
report to a format it understands. codecov detects the format
server-side. It also handles go's coverage format better: it highlights
lines with "some coverage" in yellow (coveralls has no concept of this).
