startop: app_startup script fixes for youtube/chrome

Fix remote_pkill function to work on multiple pids,
this was breaking chrome (which has 3 pids).

Fix activity inference to the "$pkg/$activity"
pattern where previously it could accidentally parse
the wrong token.

Fix app launching to handle activities with '$' in
the name which adb shell treated as a variable.

Test: manual
Change-Id: Ifc9a72f1b9bb5e1416c7602f27f4614efd003849