cli/command/container: --use-api-socket: don't write empty credentials

[thaJeztah]

• follow-up to run: flag to include the docker socket #5858

Before this patch, a valid, but empty set of credentials would still
write a config-file to the container and set DOCKER_CONFIG:

mkdir -p tmpConfig
export DOCKER_CONFIG=$PWD/tmpConfig
echo'{}'>"${DOCKER_CONFIG}/config.json"
docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
{
"auths": {}
}
echo'{"auths": {}}'>"${DOCKER_CONFIG}/config.json"
docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
{
"auths": {}
}
echo'{"auths": {"https://index.docker.io/v1/": {"auth": "am9lam9lOmhlbGxv"}}}'>"${DOCKER_CONFIG}/config.json"
docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
{
"auths": {
"https://index.docker.io/v1/": {
"auth": "am9lam9lOmhlbGxv"
}
}
}

With this patch, the DOCKER_CONFIG env-var and config-file are only created
if we have credentials to set;

mkdir -p tmpConfig
export DOCKER_CONFIG=$PWD/tmpConfig
echo'{}'>"${DOCKER_CONFIG}/config.json"
docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
cat: can't open '/run/secrets/docker/config.json': No such file or directoryecho '{"auths": {}}' > "${DOCKER_CONFIG}/config.json"docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.jsoncat: can't open '/run/secrets/docker/config.json': No such file or directory
echo'{"auths": {"https://index.docker.io/v1/": {"auth": "am9lam9lOmhlbGxv"}}}'>"${DOCKER_CONFIG}/config.json"
docker run --rm --use-api-socket alpine cat /run/secrets/docker/config.json
{
"auths": {
"https://index.docker.io/v1/": {
"auth": "am9lam9lOmhlbGxv"
}
}
}

- Human readable description for the release notes

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cli/command/container/create.go	0.00%	6 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[thaJeztah]

@Benehiko PTAL 🤗