Tests: Simplify "testTimeout" option
Tests: Remove uselss "keys" helper
Tests: Remove QUnit start hook
Tests: Simplify globals cleanup
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
Tests: Move some of the Sizzle tests to selector
Tests: Copy Sizzle.contains tests
Tests: Copy Sizzle.uniqueSort tests
Tests: Add test for selectors with commas
Tests: Add more tests for Sizzle attributes
Tests: Copy some Sizzle combinators tests
Tests: Remove unused variables
Tests: Bring back some of the clean-up logic
Tests: Fix failing ajax tests in oldIE

(cherry-picked from the 71780965072b1271018f2cf360e82fbe31f4987e)

Picked up so tests from the 1.x-master would be more similar to this branch