Bug 1070845 - [sharedtest] unit test refactoring for new version chai.assert api (rebased)

test_agent used very old version chai library version=0.5.3 in the current version=1.9.1 deepEqua
```javascript
        function onResolve(value) { 
        };

        function onReject(err) {
          assert.equal(err.message, 'invalid output dimensions');
        };

        function check(promise) {
          return promise.then(onResolve, onReject);
        };

        Promise.all([
          check(ImageUtils.resizeAndCropToCover()),
          check(ImageUtils.resizeAndCropToCover('not a blob')),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob)),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob, 0, 10)),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob, 10, 0)),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob, -10, 10)),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob, 10, -10)),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob, Infinity, 10)),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob, 10, Infinity)),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob, {}, 10)),
          check(ImageUtils.resizeAndCropToCover(self.inputBlob, 10, {}))
        ]).then(done, done); 
      });
```
```
[sharedtest-test/unit/image_utils_test.js] throw for invalid input ‣

Error: done() invoked with non-Error: ,,,,,,,,,,
    at (anonymous) (app://sharedtest.gaiamobile.org/common/vendor/mocha/mocha.js:3711:38)
    at (anonymous) (app://sharedtest.gaiamobile.org/common/test/mocha_generators.js:46:20)
```
in each image test