Work with file path including spaces

[nojimage]

When shared folder includes space char, docker-machine-nfs don't work correctly.

eg.

docker-machine-nfs default --shared-folder=/Users/nojima/Documents/Virtual\ Machines.localized/project

[INFO] Configuration:

	- Machine Name: default
	- Shared Folder: /Users/nojima/Documents/Virtual
	- Shared Folder: Machines.localized/project
	- Mount Options: noacl,async

	- Force: false
...

This patch allows to mount even paths that contain spaces.

[tonivdv]

Thanks for the contribution!