Adapt tests for last round only p+epsilon contract

[whwgeorge]

Adapt the tests (https://github.com/kleros/kleros-attacks/blob/master/test/p-epsilon.js) used to test the previous p+epsilon contract PEpsilon.sol to test the modified version (https://github.com/kleros/kleros-attacks/pull/15/files) that only pays the bribe to jurors in the last appeal round (e.g if the case turns out to ultimately be appealed three times, jurors in appeal round three can receive the same bribes as they would in PEpsilon.sol but jurors in earlier rounds cannot receive bribes).