Fix ubuntu.yml task "Enable Edge repository" to notify apt handler

[robertpeteuil]

Fixes install from the edge channel task by notifying the apt handler, instead of the yum handler.

This task only executes when running on ubuntu with docker_channel set to "edge", so it's likely that this wasn't caught during testing.

[ericsysmin]

Thank you for the commit, we've accepted into master, will be in the next release.