Allow passing of VMWare Fusion specific configuration flags

[jezell]

To optimize performance of our VMs, our Vagrant our setup would specify certain VMWare specific parameters for the vm such as:

    f.vmx["refvmx.minVmMemPct"] = "100"
f.vmx["MemTrimRate"] = "0"
f.vmx["sched.mem.pshare.enable"] = "FALSE"
f.vmx["prefvmx.useRecommendedLockedMemSize"] = "TRUE"
f.vmx["mainMem.partialLazySave"] = "FALSE"
f.vmx["mainMem.partialLazyRestore"] = "FALSE"
f.vmx["priority.grabbed"] = "high"
f.vmx["priority.ungrabbed"] = "normal"

Not seeing a way to do this with docker-machine, but it would be extremely useful.

[nathanleclaire]

cc @frapposelli