Force to use only one candidate device

[imobachgs]

Problem

After merging #268, there is a mismatch between the UI and the backend. By default, the backend selects many candidate_devices (as shown in the screenshot below).

However, the UI only allows selecting a single device. Initially, I thought about extending the UI, but as you cannot specify any volume yet, there is no point in doing selecting more than one device. Actually, the result of the current behavior, is that /dev/sdc GPT gets removed for no good reason.

Solution

I would force the use of a single device by now, so we can release the new version as soon as possible. After all, we are expected to work on the storage UI for the next-next release, so we can address this problem in a proper way.

I am proposing a solution but, to be honest, I am not sure if it is the "best" way. Please, let me know if you think we should do something different.

Testing

• Set a unit test to pending 😞
• Tested manually

Screenshots

If the fix affects the UI attach some screenshots here.

[coveralls]

Coverage increased (+0.04%) to 74.789% when pulling 7a71408 on force-one-candidate-device into 621efea on master.

[joseivanlopez]

Closing in favor of #309.