Fixed setting run_time of :class:.Succession after creating the animation object

[behackl]

Overview: What does this pull request change?

Fixes #2563, fixes #2711: For Succsession, the animation run time was not processed correctly if the run_time attribute was set after creation of the animation object. This happens, for example, if the run_time keyword argument of Scene.play is passed like this:

self.play(
    Succession(anim1, anim2, ...),
    run_time=42
)

This also supersedes #2913. I have also included a test for this fix.

[naveen521kk]

Lgtm