Refactor per loader tests

[innoavator]

For each loader, the test will be of the following format:

it('should return true on  canResolve', () => {
    const loader = new awsS3Loader();
    for (regex in array of regexes) {
       // test each regex
    }
});

it('should return false on canResolve', () => {
    const loader = new awsS3Loader();
    for (regex in array of regexes) {
       // test each regex
    }
});

it('should return required value on resolve', () => {
    const loader = new awsS3Loader();
    for (regex in map of <regex: return value>) {
       check if required value is returned
    }
});

it('should throw error on resolve', () => {
    const loader = new awsS3Loader();
    for (regex in map of <regex: return value>) {
       check if error is thrown (check throw message if possible)
    }
});