Add timeout on KargerMinCut

[jkomyno]

In KargerMinCut, the average complete execution of the algorithm takes 146 seconds (2.5 minutes), but the longest execution takes 918 seconds (15 minutes).
The longest discovery time, however, takes 45 seconds.

We can thus set a maximum execution time to 120 seconds.

We can re-use the same timeout class used for homework 2.