Add test in lockup contract about termination process

[telezhnaya]

1. Suppose we have two lockup contracts A and B that had exactly the same initialization parameters. These contracts are also interacted in exactly the same way and moment by the users, i.e. they receive the same transactions/receipts at the same moments;
2. Suppose B is getting terminated at a certain timestamp T;
3. Is the following true for any possible situation: contracts A and B will unlock exactly the same number of tokens (that also become immediately liquid/withdraw-able) at exactly the same moments from timestamp T' (T'<=T) until some timestamp T'' (T<=T''), and after timestamp T'' B will not unlock any tokens.

Me and @frol came to the conclusion that it's true, but it's better to add a test for that