bitbake: toaster: measure task duration with server-side timestamps

bitbake: toaster: measure task duration with server-side timestamps

The buildstats and toaster use separate time markers to measure the
duration of task execution. This causes a mismatch in the time
measured by buildstats class and the time measured in toaster.

The solution implemented here is to timestamp the creation of
every TaskBase event on the bitbake server side and calculate
the execution duration as the difference between creation time
of TaskSucceeded and TaskStarted events.

Based on an original patch by Marius Avram.

[YOCTO #5485]

(Bitbake rev: 7a08282c074c264f414cf7665dc873f51245072c)

Signed-off-by: Marius Avram <marius.avram@intel.com>
Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>