The unit files for test-execute are named like
`exec-(setting-name-in-lower-character)-(optional-text).service`.
However, test units for AmbientCapabilities= are not following this.
So, let's rename them for the consistency.
This does not change anything in the functionality of the test.
The nobody user/group may not synthesized by systemd.
To run tests the functionalities in such situation, this adds tests
by user/group by daemon, as it is expected to exists all environments.