Changing the message for elementsPresent. 

Changing the messaging for elementsPresent assertion. The reason behind this is that the success message is too verbose, and really we are only interested in the case where elements fail the test.

Status: **Ready to merge**

Reviewers: @kbingman @marlowpayne @mobify-derrick 

## Changes
- Changed message
- Updated tests to reflect change.

## How to test-drive this PR
- Point to this branch in a project with Nightwatch
- Run your snoop tests
- Ensure the message has changed