Previously, virtualizationservice had its own UID
`virtualizationservice`. As a result, crosvm, which is spawned by it
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,
crosvm inherits the same UID.
Bug: 223790172
Bug: 216788146
Test: watch TH
Change-Id: Ia61a86726d7aad050f2a84e8857105ad6fde33d4