test(concat): add subscription tests for concat
test(concat): add subscription tests for concat

Add tests to assert subscription/unsubscription moments for concat
operator. This also changes most tests to use cold sources instead of
hot sources, since it makes more sense to concat cold sources, because
concatenating hot sources is essentially a merge.

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