When a tagger fails, use a fallback tagger

[dgageot]

This is contributing to reduce the amount of strange error messages the user get.

• Let the git tagger fail when no git information is found.
• Use a fallback tagger (usually will tag with :latest)
• Move the errors to the debug log and show a discrete warning to the user

BEFORE:

Generating tags...
 - leeroy-web -> WARN[0000] Unable to find git commit: running [git describe --tags --always]
 - stdout:
 - stderr: "fatal: not a git repository (or any of the parent directories): .git\n": exit status 128
leeroy-web:dirty
 - leeroy-app -> WARN[0000] Unable to find git commit: running [git describe --tags --always]
 - stdout:
 - stderr: "fatal: not a git repository (or any of the parent directories): .git\n": exit status 128
leeroy-app:dirty
Checking cache...
 - leeroy-web: Found Locally
 - leeroy-app: Found Locally

AFTER:

Generating tags...
 - leeroy-web -> leeroy-web:latest (check the logs for errors)
 - leeroy-app -> leeroy-app:latest (check the logs for errors)
Checking cache...
 - leeroy-web: Found Locally
 - leeroy-app: Found Locally

Signed-off-by: David Gageot david@gageot.net

[codecov]

Codecov Report

Merging #4019 into master will decrease coverage by 0.04%.
The diff coverage is 28.57%.

Impacted Files	Coverage Δ
pkg/skaffold/runner/build_deploy.go	53.57% <23.07%> (-4.54%)	⬇️
pkg/skaffold/build/tag/git_commit.go	82.89% <100.00%> (-0.23%)	⬇️

[briandealwis]

Is it worth saying:

Suggested change

	return nil, fmt.Errorf("generating tag for %q: %w", imageName, err)
	return nil, fmt.Errorf("generating checksum as fall-back tag for %q: %w", imageName, err)