Fix ephemeral post-install launching

Provide the ephemeral installer with some additional pieces of information:
1) instead of de-referencing the URL a second time, give the installer the
   exact package name
2) instead of relying on ephemeral apps to define verified links, give the
   installer a pending intent to launch when the ephemeral is installed
3) give the installer a pending intent to launch if the installer fails,
   for whatever reason, to install the ephemeral app

Bug: 25119046
Change-Id: I45f50481caee09d5d09451e4b2492e64b0faae82