Windows + minikube + skaffold + non-elevated shell = fail

### Expected behavior

When skaffold detects that minikube's docker daemon can't be resolved (as the warning shows as well) it should either:
- fail when `build.local.push = false` is setup
- force `build.local.push =true` when it is not setup

### Actual behavior

Skaffold fails to find the minikube docker daemon and hence creates a deployment inside minikube that relies on a non-existent image (as it is not pushed):

```
C:\Users\balintp\dev\proj\skaffold\examples\getting-started>skaffold dev
time="2019-10-16T15:16:04-07:00" level=warning msg="Could not get minikube docker env, falling back to local docker daemon: getting minikube env: Running [minikube docker-env --shell none]: stdout , stderr: X The docker host is currently not running\n, err: exit st
atus 69: exit status 69"
Generating tags...
- gcr.io/k8s-skaffold/skaffold-example -> gcr.io/k8s-skaffold/skaffold-example:v0.40.0-58-gd4bd5978-dirty
Tags generated in 413.9981ms
Starting build...
Found [minikube] context, using local docker daemon.
Building [gcr.io/k8s-skaffold/skaffold-example]...
Sending build context to Docker daemon 3.072kB
Step 1/6 : FROM golang:1.12.9-alpine3.10 as builder
---> e0d646523991
Step 2/6 : COPY main.go .
---> Using cache
---> 2015d9353f14
Step 3/6 : RUN go build -o /app main.go
---> Using cache
---> 0597b5dcee83
Step 4/6 : FROM alpine:3.10
---> 961769676411
Step 5/6 : CMD ["./app"]
---> Using cache
---> a42bf125a1f1
Step 6/6 : COPY --from=builder /app .
---> Using cache
---> 1cf52c839515
Successfully built 1cf52c839515
Successfully tagged gcr.io/k8s-skaffold/skaffold-example:v0.40.0-58-gd4bd5978-dirty
Build complete in 840.0648ms
Starting test...
Test complete in 1.0005ms
Starting deploy...
kubectl client version: 1.14
pod/getting-started created
Deploy complete in 2.2762852s
Watching for changes...
rpc error: code = Unknown desc = Error response from daemon: manifest for gcr.io/k8s-skaffold/skaffold-example:1cf52c83951577b49c247f19583544e0686629c14245777fd91502cf6488c2e0 not found
Back-off pulling image "gcr.io/k8s-skaffold/skaffold-example:1cf52c83951577b49c247f19583544e0686629c14245777fd91502cf6488c2e0"
rpc error: code = Unknown desc = Error response from daemon: manifest for gcr.io/k8s-skaffold/skaffold-example:1cf52c83951577b49c247f19583544e0686629c14245777fd91502cf6488c2e0 not found
```

### Information

- Skaffold version: master (0.40+)
- Operating system: Windows 10 Enterprise
- Contents of skaffold.yaml: getting started example

### Steps to reproduce the behavior

Run Skaffold in a non-admin powershell window against a hyperv minikube instance (that needs admin rights):

1. getting-started example
2. `skaffold dev`