Add config parameter for the cri socket path

[afbjorklund]

Closes #3153

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[dlorenc]

Looks like some failing tests in travis:

    	kubeadm_test.go:245: actual config does not match expected.  actual:

[afbjorklund]

Not sure if cri-socket should be a top-level citizen, but it was that way in kubeadm...
The current complementary configuration options are the other hand totally low-level ?

    --extra-config=kubelet.container-runtime=remote \
    --extra-config=kubelet.container-runtime-endpoint=/var/run/crio/crio.sock \
    --extra-config=kubelet.image-service-endpoint=/var/run/crio/crio.sock \

Will look at the test suites.

[afbjorklund]

It seems that it inserted a newline, so I suppose the template needs to be modified slightly...

FAIL k8s.io/minikube/pkg/minikube/bootstrapper/kubeadm 0.154s

[afbjorklund]

ok k8s.io/minikube/pkg/minikube/bootstrapper/kubeadm 0.141s

[afbjorklund]

Note that kubeadm chokes on unix:// since it is "not an absolute path"...

[RA489]

@afbjorklund this PR needs rebase.