firstboot: synchronously wait for systemd-vconsole-setup.service/restart job

firstboot: synchronously wait for systemd-vconsole-setup.service/restart job

Requested in https://github.com/systemd/systemd/pull/27755#pullrequestreview-1443489520.

I dropped the info message about the job being requested, because we get
fairly verbose logs from starting the unit, and the additional message isn't
useful.

In the unit, the ordering before systemd-vconsole-setup.service is dropped,
because now it needs to happen in parallel, while systemd-firstboot.service
is running. This means that we may potentially execute vconsole-setup twice,
but it's fairly quick, so this doesn't matter much.