[CRTP infra-vmware connector]Storagelink : add action mount and unmount on extension and connector

[cgourdin]

On storagelink (system disk), there's no actions. Add the action mount() and unmount() via a mixin on extension + connector code.
Don't forget, the connector must be useable with infrastructure extension and with all other child extensions.

The use of a schell script may be required (via ssh).
The methods mount/unmount must be compliant with linux firstly and windows after.

[cgourdin]

Not useful for now, but will be a great improvement if needed in future. To see with Scalair use case.