Allow debugging only for apps forked from zygote

When starting the runtime from app_process, we only pass JDWP options
if starting zygote. It prevents from opening a JDWP connection in
non-zygote programs while Android apps (forked from zygote) remain
debuggable.

Bug: 23050463

(cherry picked from commit 7a09b832)

Change-Id: Ib5b6d3bc4d45389993c3c54226df5a7b72479d19