Add request to import VMDKs as cubes (Fusion/WS)

The VMX generation code is way too simple, but I can move
forward with this without having to write a proper VMX reading/writing
library.

Added example and some tests.
vmx keys are case insensitive

Make sure we only deal with lowercase case so we don't duplicate them.
loaded VMX keys are lower case
test fixes
Merge pull request #23 from rubiojr/vmdk-local-cubes

Add request to import VMDKs as cubes (Fusion/WS)