Add user probe callbacks

[imobachgs]

Problems

• Indirectly, StorageManager is coupled with UI. The IssuesManager#report_probing_issues is called if an issue is registered during the probing phase (see manage_probing_issues method.
• While analyzing the problem, we discovered that the Devicegraph contains a IssuesManager instance. This class just adds some UI logic on top of an IssuesList, so holding a reference in our data model looks tricky.

Solution

To decouple the UI from the probing process, we decided to rely on the callbacks mechanism. However, we found out that there are two use-cases for those callbacks:

• Use them to augment our data model, as we do currently (adding the issues to the Devicegraph).
• Redefine the UI interaction.

So instead of just extending the Callbacks::Probe, we decided to keep this class as an implementation details and inject a new callback class.

At this point, it only implements a #report_probing_issues method and the API is still under discussion. Event the method name looks redundant (why about just report_issues?).

Last but not least, we decided to get rid of the IssuesManager class, as it is not needed by the Devicegraph class anymore.

To do

• [x] Discuss the current API
• [x] Should we consider doing the same for the activation? Perhaps we could open a separate PBI. By now, let's keep as they are.

[coveralls]

Coverage decreased (-0.02%) to 97.807% when pulling 75576ab15a46630bb10ea7c075634d1728f29d14 on add-user-probe-callbacks into 24a7faa45d27139ddc141bc09d50b34b3d699c7b on master.

[yast-bot]

:heavy_check_mark: Public Jenkins job #443 successfully finished :heavy_check_mark: Created OBS submit request #1006181

[yast-bot]

:heavy_check_mark: Internal Jenkins job #229 successfully finished :heavy_check_mark: Created IBS submit request #280769