Decrease maximum time to wait for a mirror process to finish from 1 day to 2 hours

This MR proposes to decrease the time that GitLab waits before to mark a mirror update process stuck as failed.
Full description of the scenario in #1093 (closed)
Now this time is one day. When the problem happens, the user sees during one day that the project was updating from upstream.
If a project has been updating from a remote for longer than 2 hours, we could conclude that something went wrong, mark the mirror as failed and retry next time.

Closes #1093 (closed)