Enable core platform API warnings on non-user builds

Core platform API violation reporting is disabled by default and can be
enabled by setting the persist.debug.dalvik.vm.core_platform_api_policy
property. Set it to "just-warn" for non-user builds and leave disabled
on user builds.

Test: builds, boots
Bug: 125701194
Change-Id: I2f4be42373de9fdbc71c3178de6d34e07809f13a