Allow dev/shm size to be configurable in the native driver

Fixes #2606

Right now it's hard coded to a -o option.  I don't know if this is the
best way to do it because the hard coding fs.system.shm.size=512m could
lead to duplication but I like being explicit and with this way we can
easily see all the commands that are supported by the drivers.

I'm up to suggestions on how to handle this?  


Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)