test(zip): subscription asserts for static zip
test(zip): subscription asserts for static zip

Add tests for Observable.zip that assert subscription and unsubscription
times. Also "normalize" the tests to contain all tests from the instance
variant of zip.

figueredo/RxJS,gluck/RxJS,benlesh/RxJS,benlesh/RxJS,saneyuki/RxJS,jinroh/RxJS,mattpodwysocki/RxJS,trxcllnt/RxJS,adrianomelo/RxJS-1,Brocco/RxJS,jayphelps/rxjs,trxcllnt/RxJS,robwormald/RxJS,kwonoj/RxJS,kwonoj/RxJS,SangKa/RxJS-Docs-CN,adrianomelo/RxJS-1,justinwoo/RxJS,ReactiveX/RxJS,Brocco/RxJS,gluck/RxJS,jayphelps/rxjs,jadbox/RxJS,IgorMinar/RxJS,adrianomelo/RxJSNext,elliotschi/rxjs,jayphelps/rxjs,robwormald/RxJS,Brocco/RxJS,jinroh/RxJS,trxcllnt/RxJS,trxcllnt/RxJS,jayphelps/rxjs,figueredo/RxJS,ReactiveX/rxjs,mattpodwysocki/RxJS,martinsik/rxjs,adrianomelo/RxJSNext,IgorMinar/RxJS,SangKa/RxJS-Docs-CN,Brocco/RxJS,Igorbek/rxjs5,jinroh/RxJS,jadbox/RxJS,elliotschi/rxjs,staltz/RxJSNext,mattpodwysocki/RxJS,kwonoj/RxJS,adrianomelo/RxJS-1,figueredo/RxJS,mattpodwysocki/RxJS,RxJS-CN/RxJS-Docs-CN,jadbox/RxJS,jayphelps/rxjs,ReactiveX/RxJS,martinsik/rxjs,kwonoj/RxJS,SangKa/RxJS-Docs-CN,justinwoo/RxJS,robwormald/RxJS,gluck/RxJS,gluck/RxJS,staltz/RxJSNext,ReactiveX/rxjs,ReactiveX/rxjs,benlesh/RxJS,Igorbek/rxjs5,Igorbek/rxjs5,elliotschi/rxjs,robwormald/RxJS,adrianomelo/RxJS-1,Igorbek/rxjs5,jadbox/RxJS,RxJS-CN/RxJS-Docs-CN,benlesh/RxJS,martinsik/rxjs,justinwoo/RxJS,adrianomelo/RxJSNext,ReactiveX/rxjs,ReactiveX/RxJS,SangKa/RxJS-Docs-CN,RxJS-CN/RxJS-Docs-CN,staltz/RxJSNext,RxJS-CN/RxJS-Docs-CN,ReactiveX/RxJS,adrianomelo/RxJSNext,saneyuki/RxJS,figueredo/RxJS,jinroh/RxJS,staltz/RxJSNext,martinsik/rxjs,justinwoo/RxJS,elliotschi/rxjs