[infra] Move app installation to install method

This generally makes things tidier (e.g. perf_skottietrace.py no longer
needs special logic so that the app is only installed once), and it
means iOS can install only the app that's going to be run instead of
installing everything.

Change-Id: Ic07c56e724d0379255c8da5f204d9d6379b646ec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/273002
Commit-Queue: Ben Wagner aka dogben <benjaminwagner@google.com>
Auto-Submit: Ben Wagner aka dogben <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
67 files changed