dumpstate: fix dumping traces for vm processes on 64-bit

dumpstate was not dumping any stack traces for vm processes because
it was failing the string compare for /system/bin/app_process.
64-bit devices use app_process32 and app_process64 instead of
app_process, and zygote64 alongside zygote.  Change the string
matching to be prefix matching.

(cherry picked from commit 8eb25d55)

Change-Id: I6b1568161fae278f0e6107990e5b750cf0ca902b