Reapply "Migrate the blkio controller to the v2 cgroup hierarchy"

This reverts commit c7a6fe68.
Repply the blkio controller migration because it was not responsible
for the test failures that led to the revert. See also the following bugs:
* https://b.corp.google.com/issues/260143932
  (v2/android-virtual-infra/test_mapping/presubmit-avd test failure)
* https://b.corp.google.com/issues/264620181


  (CtsInitTestCases.RebootTest#StopServicesSIGKILL failure)

The only change compared with the previous version is that the io
controller has been declared optional. This is necessary because some
devices have a kernel that does not support the io controller.

Bug: 213617178
Test: Cuttlefish and various phones
Change-Id: I490740e1c9ee4f7bb5bb7afba721a083f952c8f2
Signed-off-by: Bart Van Assche <bvanassche@google.com>