Fix the cgroup directory owner in createProcessGroupInternal()

Without this patch attempts to modify the blkio cgroup attributes by
/system/bin/mediaserver fail as follows:

03-23 09:27:59.542   517  1811 E libprocessgroup: Failed to write '100' to /sys/fs/cgroup/./uid_1013/pid_517/io.bfq.weight: Permission denied

This is because the mediaserver process is started as user 'media',
because the mediaserver process is not in the system group and hence
does not have permission to write into a directory with the following
owner, group and permissions:

vsoc_x86_64:/ # ls -ld /sys/fs/cgroup/./uid_1013/pid_517/io.bfq.weight
-rwxrwxr-x 1 system system 0 2022-03-23 09:27 /sys/fs/cgroup/./uid_1013/pid_517/io.bfq.weight

Bug: 213617178
Test: Booted Android in Cuttlefish and inspected logcat.
Change-Id: I788acc9a137ae29898177f492cae2f954a9c811c
Signed-off-by: Bart Van Assche <bvanassche@google.com>