Virtualizationservice is owned by the system UID

Previously, virtualizationservice had its own UID
`virtualizationservice`. As a result, crosvm, which is spawed by
virtualizationservice`, also run as the UID. However, that prevented us
from applying task profiles to the crosvm process because joining a
process to a cgroup requires system UID.

To fix that, virtualizationservice now runs as system UID. As a result,
this directory that virtualizationservice accesses has to change its
owner and group to system.

Bug: 223790172
Bug: 216788146
Test: watch TH

Change-Id: I2bdf49e99f1841bf77ff046b0c2455064b174e0a