docker driver: Improve error message on Linux with when docker socket is inaccessible

[balopat]

On a fresh docker installation in Linux - I haven't yet set the docker group up - hence I would need to use sudo - however if I don't know this, I got this error message which is misleading:

• it says to restart docker desktop 1) I'm on Linux - there is no Docker Desktop here 2) this is not the issue, the issue is the permission denied problem on the socket

We should report "Minikube can't access the Docker daemon, permission is denied. Suggestion: create the docker group to allow access and add $user to the group with sudo usermod -aG docker $USER" or something similar

minikube start --vm-driver=docker
😄  minikube v1.8.2 on Debian 9.11
✨  Using the docker driver based on user configuration

❗  'docker' driver reported an issue: exit status 1
💡  Suggestion: Docker is not running or is responding too slow. Try: restarting docker desktop.

💾  Downloading preloaded images tarball for k8s v1.17.3 ...
    > preloaded-images-k8s-v1-v1.17.3-docker-overlay2.tar.lz4: 499.26 MiB / 499
E0411 00:53:33.476159   13010 cache.go:106] Error downloading kic artifacts:  error loading image: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.24/images/load?quiet=0: dial unix /var/run/docker.sock: connect: permission denied
🔥  Creating Kubernetes in docker container with (CPUs=2) (0 available), Memory=2200MB (0MB available) ...

💣  Unable to start VM. Please investigate and run 'minikube delete' if possible: creating host: create: creating: create kic node: creating volume for minikube container: output Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.40/volumes/create: dial unix /var/run/docker.sock: connect: permission denied
: exit status 1

😿  minikube is exiting due to an error. If the above message is not useful, open an issue:
👉  https://github.com/kubernetes/minikube/issues/new/choose

[medyagh]

we fixed this a few commits ago, this should be on the HEAD

@balopat

[medyagh]

dupe of #7457 please let me know if the issue is still there

[afbjorklund]

Seems like duplicates:

1. Docker Desktop on Linux Getting Started for Linux suggests non-existing Docker Desktop #7440
2. docker.sock permission denied dial unix /var/run/docker.sock: connect: permission denied #7566

[afbjorklund]

we fixed this a few commits ago, this should be on the HEAD

Now it looks like:

❗  'docker' driver reported an issue: "docker version --format {{.Server.Version}}" exit status 1: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.40/version: dial unix /var/run/docker.sock: connect: permission denied
💡  Suggestion: 
📘  Documentation: https://minikube.sigs.k8s.io/docs/drivers/docker/

💣  Failed to validate 'docker' driver