Report more details on task progress

[mgrabovsky]

The task status Retrace Server currently reports to the user is somewhat short on information content. Basically, it only reports (roughly) the phase in which the task is currently running (analysing crash data, generating backtrace etc.) and the result (failure, success). Since task status is obtained by polling, this results in long stretches of apparent inactivity in reporting UIs (abrt-retrace-client, report-cli, report-gtk) when retracing large coredumps, which may lead users to believe that the process got stuck.

For a smoother user experience, we would need at least a crude progress indicator, e.g. a gauge in the range 0–100%, of each phase or overall.

Most or all of the information necessary for such an indicator should be available from the output of the commands Retrace Server runs. The two most time consuming phases are coredump analysis (which is done by Retrace Server's coredump2packages) and downloading/installing packages (DNF). The rest are comparatively much faster and thus practically negligible.