Tests: Remove Sizzle intergration tests

Fixes #14818
Tests: More improvments for testrunner

Conform to style guide and simplify it
Build: Use jscs to check test helpers

Also fix issues found by jscs
Build: Add lint task
Tests: Correct logic of a broken assertion
Tests: Improve jsonp tests

Since global variable for callback always would be equal to undefined value
it better to check for boolean instead
Tests: Do global clean up in teardown function