fix(upgrade): fixes erroneous values in the list of processed upgrades

Code in the upgrade includes was overwriting variables in the upgrade service
resulting in an object being saved to the list of processed upgrade where the
filename should have been. This upgrade replaces the class with the filename and
isolates the scope of the include so upgrades cannot break the process.

Fixes #7198.
Nice, I dowload the file, and do the test again : 
On the existing 1.9 instance, I update the files with mrclay's Fork, and after doing an upgrade, the mesage still appears, on other lines (237 and 149 of /engine/classes/Elgg/UpgradeService.php)

BUT
On the working elgg1.8 instance, if I do the upgrade procedure with the new tarball, I don't have the error message anymore.