Add hook for JVMTI agent in system server

Add a place to attach a jvmti agent into the system server in debug
builds.  This allows profiling and other investigations for performance
improvements.

Bug: none
Test: attach agent, collect result
Change-Id: I299dffb1774fdce48b9b695a614b7ab60f1307e2
Merged-In: I299dffb1774fdce48b9b695a614b7ab60f1307e2
(cherry picked from commit 1a88539d)