Let blkio cgroup follow cpuset cgroup only

Some app may have different cgroup settings in cpuset and schedtune for its
threads, so let blkio follow cpuset only, which represents the app's current
state more accurately. Otherwise, if that thread is doing IO, then its
performance will be affected because its blkio group is in lower priority
group as schedtune.

ex: an app is now in top-app, but some thread of it set schedtune group to
background, and blkio follows schedtune because it is called later.

Main thread:
6:schedtune:/top-app
5:memory:/
4:cpuset:/top-app
3:cpuacct:/uid_1000/pid_8766
2:cpu:/
1:blkio:/
0::/

Some thread:
6:schedtune:/background
5:memory:/
4:cpuset:/top-app
3:cpuacct:/uid_1000/pid_8766
2:cpu:/
1:blkio:/background
0::/

Bug: 124727032
Test: blkio has same settings with cpuset
Change-Id: I9a140c7d9d93e1dd43c34c8cf066f4a62e2bf604
Merged-In: I9a140c7d9d93e1dd43c34c8cf066f4a62e2bf604