cgroup follow for procs in the same cgroup.procs

For Android processes, cgroup is managed by AMS, when AMS change cgroup
of a task, AMS ignored processes in the same process group cgroup.procs
if a foreground app call fork at JNI and then switch to background,
children processes will keep foreground priority and out of control

dex2oat is a real world example that foreground app call exec dex2oat to
compile dexfile, when the parent process switch to background cgroup,
dex2oat will not follow it, foreground cgroup allows background dex2oat
hold huge of CPU resources, it may impact UX of foreground apps

With this change, the cgroup of children processes will follow its
parent if they are in the same cgroup.procs

Properties to control:
ro.vendor.qti.cgroup_follow.enable to enable/disable this feature
ro.vendor.qti.cgroup_follow.dex2oat_only to use for all or dex2oat only

Change-Id: Ibb7c4a451dfad6615a04d1f894ede22c7adb8ec9
CRs-Fixed: 2139112