Bug 1070487 - [keyboard] unit test refactoring for new version chai.assert api

test_agent used very old version chai library version=0.5.3
in the current version=1.9.1 same api chenged 

1. assert.length -> assert.lengthOf
2. in new version assert.deepEqual take prototype into consideration same test need change

this compatible with both old and new version chaijs library
Please update the comment to:
UserPress would have updateCoords() defined in prototype, so cannot use 'deepEqual' with lastest chai.js.