Reprobe storage on network devices changes

[joseivanlopez]

Now D-Installer is able to configure iSCSI devices. And more technologies like FCoE is expected to be added too. With the current implementation, the storage devices are not automatically probed when an iSCSI session is created or closed. This is specially problematic when a session is closed and the storage proposal was using such a device.

Most likely we will need a button for reprobing in the UI, but still we need to add some kind of proposal validation to avoid continuing with the installation if the proposal is using an invalid device.

A possible solution might be to check whether the candidate devices are still present in the system. For that, we need to ask to libstorage-ng for reprobing the system. Ideally, such a reprobing should be performed without changing the current devicegraphs. Otherwise, we need to recalculate the proposal everytime we want to validate it. Libstorage-ng already provides a light probe, but that method only returns whether some devices where found in the system. We need it to return some more information, for example the SSID of the detected devices.

Having such an special probing, our validation would consist on checking whether the SSID of the cadidate devices are still in the list of SSIDs provides by the fast probing. This solution would be generic enough for any technology that implies adding and removing devices.

[ancorgs]

We plan to improve this (see #498), but #484 is good enough for closing this.