feat(TestScheduler): Add subscription schedule to expectObservable

[gstamac]

Description:

Related issue (if exists):

[coveralls]

Coverage increased (+0.0007%) to 97.545% when pulling 02f185e on gstamac:master into 556c904 on ReactiveX:master.

[kwonoj]

Appreciate for sending out PR! Unfortunately, we are currently in discussions of revising interface around test scheduler
(https://github.com/ReactiveX/rxjs-core-notes/blob/master/rxjs/2018/2018-02/february-28.md#discussed / #3231) and holding off updating existing interfaces meanwhile and let new interface exists in parallel for migration purpose. Please feel freely check out issues with related projects and share opinions if needed.

[gstamac]

Please reconsider adding this PR. It is a minor contribution which doesn't change any API. It just implements something that should be there already. I really need this and it's really annoying to modify rxjs with every update.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.