Add commit callbacks to inst_prepdisk

[joseivanlopez]

Problem

Agama uses the inst_prepdisk client to perform the required storage actions. That client calls to the storage commit action, which uses the default commit callbacks from YaST to report the errors.

Agama needs to provide its own callbacks, see https://github.com/openSUSE/agama/pull/558.

Solution

Allows to pass commit callbacks to the inst_prepdisk client.

[coveralls]

Coverage: 97.75% (+0.0002%) from 97.75% when pulling 63538539c38e0b2856f3b633c24534c322248630 on joseivanlopez:commit-callbacks into 2bd8630c6c5766d177a08a8fcb0188f594d501cc on yast:master.

[yast-bot]

:heavy_check_mark: Public Jenkins job #463 successfully finished :heavy_check_mark: Created OBS submit request #1085053