minikube start -- allow additional arguments to --mount-string

[cmeyertons]

Is this a BUG REPORT or FEATURE REQUEST? (choose one):
I'm leaning towards bug report as I would expect --mount-string to mimic minikube mount

Please provide the following details:

Environment:

Minikube version (use minikube version): v0.32.0

• OS (e.g. from /etc/os-release): Windows 10
• VM Driver (e.g. cat ~/.minikube/machines/minikube/config.json | grep DriverName): hyperv
• ISO version (e.g. cat ~/.minikube/machines/minikube/config.json | grep -i ISO or minikube ssh cat /etc/VERSION): v0.32.0
• Install tools:

What happened:
Additional mount arguments passed into --mount-string are ignored
Ran

minikube start --mount --mount-string="C:\mydrive:/mydrive --uid 911 --gid 911 --9p-version=9p2000.L"
minikube ssh
ls -l /mydrive

What you expected to happen:
expected it to properly set ownership of /mydrive to 911 as a workaround to #2290

How to reproduce it (as minimally and precisely as possible): see what happened

[tstromberg]

Dupe of #3327