Better test failure messages

Added a bit of useful information for test error messages. Changed from: 


      1) <indent-with> on a tab-indented file enforces array literal indentation:
     
      AssertionError: [object Object]
          at Function.assert.fail (/Users/fonda/work/tslint/node_modules/chai/lib/chai/interface/assert.js:58:11)

to

      1) <indent-with> on a tab-indented file enforces array literal indentation:
         AssertionError: expected failure not found on [114, 1]