Use Y2NfsClient::Widgets::NfsForm instead of NfsClient4Part

[ancorgs]

Problem

This pull request replaces #1282 (same content but with clear history)

Traditionally, the management of NFS shares in the YaST Partitioner has been a bit rough. The Partitioner never really provided its own UI to add/edit/delete NFS mounts. Instead, it executed an embedded version of yast2-nfs-client. That has always been problematic. For example, there were non-obvious problems when the same NFS share was mounted more than once in the current system in two different locations (admittedly a very uncommon scenario).

But the situation became much worse with the revamp of the interface done for SLE-15-SP3 (and openSUSE Leap 15.3). Since that moment, NFS management was completely inconsistent with the rest of the Partitioner interface:

• The NFS mounts were not displayed in the left tree (like it happens with all other devices).
• It was impossible to use the menu to access to the NFS-related actions.
• The NFS section of the Partitioner just behaved in a completely different way compared to all other tables (different buttons ordered and activated in a different way, forms in pop-ups instead of full-screen dialogs, validations at incorrect points of the workflow...)

Solution

This pull request goes together with yast/yast-nfs-client#105

With this pull request and the corresponding yast-nfs-client one mentioned above, the integration between both YaST modules is done in a more sensible way. All the functionality is still available, but in a way in which the integration is completely transparent offering a consistent user experience.

Testing

• Tested manually
• Adapted some new unit tests... BUT not as many as it would be desirable.
• Rest of tests added at Tests for the recent code #1284 (we wanted to merge this PR because of a SLE-15-SP4 beta deadline, so we delayed the tests to that another PR).

[coveralls]

Coverage decreased (-0.3%) to 97.423% when pulling 6467edb on ancorgs:nfs_form into 012b35c on yast:master.

[joseivanlopez]

LGTM

[yast-bot]

✔️ Public Jenkins job #426 successfully finished
✔️ Created OBS submit request #950832

[yast-bot]

✔️ Internal Jenkins job #219 successfully finished
✔️ Created IBS submit request #263911