Shorten trampoline toast text

Due to new toast UI constraints. So, instead of package name (which was
less informative) we display the app label now with reduced messages:

* targetSdk S+: https://screenshot.googleplex.com/3zYrPoNkNK2XabU
* targetSdk < S: https://screenshot.googleplex.com/rpMsrkr2PRWMG3z

Bug: 167676448
Test: Trigger trampoline w/ targetSdk S and < S, check toast fits.
Change-Id: Ie03cfb9668c580018835919091acadce2fea4d75