manager: tell correctly if the manager is booting

manager: tell correctly if the manager is booting

The assumption that the initial job is the job with id==1 is incorrect.
Some jobs may be enqueued before the job that starts the default unit as
in this example:

 -.mount changed dead -> mounted
 Trying to enqueue job quotacheck.service/start/fail
 Installed new job quotacheck.service/start as 1
 Installed new job systemd-stdout-syslog-bridge.socket/start as 2
 Enqueued job quotacheck.service/start as 1
 Trying to enqueue job quotaon.service/start/fail
 Installed new job quotaon.service/start as 5
 Enqueued job quotaon.service/start as 5
 Activating default unit: default.target
 Trying to enqueue job graphical.target/start/replace

This fixes a bug where displaying of boot status messages was turned off
too early.