Skaffold will always return error adding artifacts to cache when builds are not local

[ricardo-larosa]

Expected behavior

Cache is populated with built artifacts avoiding rebuilding images every time
Related to #4842 and #4753

Actual behavior

WARN[0087] error adding artifacts to cache; caching may not work as expected: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? 

Information

• Skaffold version: v1.14/v1.15
• Operating system: linux/macos
• Contents of skaffold.yaml: Any configuration with no local build
  Example:

profiles:
- name: oncluster
  build:
    artifacts:
    - image: registry.whatever/image-name
      kaniko:
        image: gcr.io/kaniko-project/executor:v1.0.0
        flags: 
          - --snapshotMode=redo
          - --verbosity=info
    cluster:
      annotations:
        sidecar.istio.io/inject: "false" # if you are not running istio comment it
      dockerConfig: 
        secretName: my-dockerconfigjson # is Opaque
      namespace: default

Steps to reproduce the behavior

1. Use a profile oncluster that builds images remotely (kaniko, etc..)
2. Run build -p oncluster --cache-file /a/local/path --verbosity trace
3. Everything runs ok
4. Cache file is populated with latest build image
   Now repeat, but before step 2 stop your local docker deamon
   you will get this error:

WARN[0087] error adding artifacts to cache; caching may not work as expected: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? 

and the cache file is not populated