minikube: minikube using hyperkit fails to restart on macOS due to stale PID-file after a reboot/shutdown

Is this a BUG REPORT or FEATURE REQUEST? (choose one): BUG REPORT

Please provide the following details:

Environment: macOS Sierra 10.12.6

Minikube version (use minikube version): v0.25.0

• OS (e.g. from /etc/os-release): macOS Sierra 10.12.6
• VM Driver (e.g. cat ~/.minikube/machines/minikube/config.json | grep DriverName): hyperkit
• ISO version (e.g. cat ~/.minikube/machines/minikube/config.json | grep -i ISO or minikube ssh cat /etc/VERSION): minikube-v0.25.1.iso
• Install tools: N/A (homebrew)
• Others: The above can be generated in one go with the following commands (can be copied and pasted directly into your terminal):

minikube version
echo "";
echo "OS:";
cat /etc/os-release
echo "";
echo "VM driver": 
grep DriverName ~/.minikube/machines/minikube/config.json
echo "";
echo "ISO version";
grep -i ISO ~/.minikube/machines/minikube/config.json

What happened: Run minikube -p proj start --log_dir /Users/XXX/.minikube/logs --loglevel 0 --vm-driver=hyperkit --memory 6144. Never completes (waited 45 minutes). Output is

Starting local Kubernetes v1.9.0 cluster...
Starting VM...

What you expected to happen: return with a shell prompt and have minikube -p proj status return Running instead of Stopped

How to reproduce it (as minimally and precisely as possible): Reboot mac while minikube is running, then do the start command above.

Output of minikube logs (if applicable): does not return anything, also hangs. Log file (~/.minikube/logs/minikube.[hostname].[user].log.INFO.[timestamp]) contains:

I0221 09:34:16.706330   48704 cluster.go:74] Skipping create...Using existing machine configuration
I0221 09:34:16.706963   48704 cache_images.go:79] Successfully cached all images.
I0221 09:34:16.963453   48704 cluster.go:83] Machine state:  Stopped

Anything else do we need to know: