provisioner: only reload docker if necessary, don't install curl

[tstromberg]

This modernizes the provisioner in three important ways:

• Only calls systemctl reload/restart if docker file has been updated - fixes docker: excessive systemctl reload/restarts #7103
• Adds it's own NewSystemdProvisioner to avoid unnecessary apt-get commands to install curl.
• Uses glog for consistency with rest of minikube codebase

This PR improves "minikube start" performance on an already running cluster by a second or so.

[k8s-ci-robot]

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[codecov-io]

Codecov Report

Merging #7115 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7115      +/-   ##
==========================================
- Coverage   37.19%   37.14%   -0.05%     
==========================================
  Files         146      146              
  Lines        9106     9118      +12     
==========================================
  Hits         3387     3387              
- Misses       5303     5315      +12     
  Partials      416      416              

Impacted Files	Coverage Δ
pkg/minikube/machine/client.go	38.46% <ø> (ø)
cmd/minikube/cmd/docker-env.go	37.30% <0.00%> (-1.87%)	⬇️
cmd/minikube/cmd/start.go	37.31% <0.00%> (-0.39%)	⬇️

[tstromberg]

/ok-to-test

[minikube-pr-bot]

Error: running mkcmp: exit status 1

[afbjorklund]

The "curl" package is being installed, because the default install command is curl | sh

func installDockerGeneric(p Provisioner, baseURL string) error {
	// install docker - until cloudinit we use ubuntu everywhere so we
	// just install it using the docker repos
	if output, err := p.SSHCommand(fmt.Sprintf("if ! type docker; then curl -sSL %s | sh -; fi", baseURL)); err != nil {
		return fmt.Errorf("error installing docker: %s", output)
	}

	return nil
}

However, the curl package is a part of the regular Ubuntu cloud images nowadays.