feat(storage): more accurate info about resizing

[joseivanlopez]

Problem

The information about resizing devices shown by the UI for finding free space is not 100% accurate. Sometimes it allows selecting to resize a device but the device cannot be resized.

Solution

• D-Bus provides more accurate information about resizing.
• The UI does not allow selecting "resize" if the device cannot be resized.
• The UI offers a button to show information about the device (either reasons why it cannot be shrunk or total shrinkable size).

Toggle screenshots

[coveralls]

coverage: 71.382% (-0.03%) from 71.408%
when pulling daadd77 on joseivanlopez:resize-improvements
into 7101d0d on openSUSE:master.

[coveralls]

coverage: 71.382% (-0.03%) from 71.408%
when pulling 12b276c on joseivanlopez:resize-improvements
into 7101d0d on openSUSE:master.

[coveralls]

coverage: 71.382% (-0.03%) from 71.408%
when pulling 12b276c on joseivanlopez:resize-improvements
into 7101d0d on openSUSE:master.

[imobachgs]

It looks good, just some minor comments (and a small bug).

[dgdavid]

Thanks @joseivanlopez! Web front-end part LGTM 👍

[joseivanlopez]

Shouldn't we also honor DeviceShrinking at the proposal settings conversion when :resize is chosen as policy?

I fear that piece of code can generate potentially dangerous :resize actions that wouldn't be accepted if configured manually. Or are we maybe safe because the proposal will ignore those? If that's the case, I would like to at least see a comment about it.

I fear we are not safe in all scenarios. For example, I was able to resize a device with closed LUKS.

[coveralls]

coverage: 71.389% (-0.02%) from 71.408%
when pulling 8d4d7c2 on joseivanlopez:resize-improvements
into 05e7963 on openSUSE:master.

[ancorgs]

LGTM