Added deletedAt buster tests borrowed from @gustawpursche

In connection with #545 @gustavpursche did a couple of extra tests for deletedAt. Basically just a copy-pasta from https://github.com/gustavpursche/sequelize/commit/13c98e6a8df1a58343ebc9ee540691948ffa06ec and deleted the corresponding jasmine test in a feeble attempt to reduce test duplication