manager: print status text of the service when waiting for a job

This does two semi-independent but interleaved things: firstly, the manager now
prints the status text (if available) of a service when we have a job running
for that service and it is slow. Because it's hard to fit enough info on the
line, we only do this if the output mode uses unit names. The format of the
line "… job is running for …" is changed to be shorter. This way we can
somewhat reasonably fit two status messages on one line.

Secondly, the manager now sends more information using sd_notify. This mostly
matters for in case of the user manager. In particular, we notify when starting
one of the special units. Without this, when the system manager would display a
line about waiting for the user manager, it would show status like "Ready.",
which is confusing. Now it'll either show something like "Started special unit
shutdown.target", or the line about waiting for a user job.

Also, the timeouts for the user manager are lowered: the user manager usually
(always?) has status disabled, so we would wait for 25 seconds before showing
job progress. Normally we don't expect to have any jobs that take more than a
second. So let's start the progress output fairly quickly, like we would if
status showing was enabled. This obviously makes the output in the system
manager about the user manager more useful. The timeouts are "desynchronized"
by a fraction so if there are multiple jobs running, we'll cycle through
showing all combinations.

Example output:

         Stopping user@1000.service...
[  OK  ] Stopped dracut-shutdown.service.
[  OK  ] Stopped systemd-logind.service.
[  OK  ] Stopped systemd-logind.service - User Login Management.
[*     ] Job user@1000.service/stop running (2s / 2min): (1 of 2) User job slowstop.service/stop running (1s / 1min 30s)...
[***   ] Job user@1000.service/stop running (3s / 2min): (2 of 2) User job slowstop2.service/stop running (2s / 1min 30s)...
[   ***] Job user@1000.service/stop running (4s / 2min): (1 of 2) User job slowstop.service/stop running (4s / 1min 30s)...
[     *] Job user@1000.service/stop running (5s / 2min): (1 of 2) User job slowstop.service/stop running (5s / 1min 30s)...
[   ***] Job user@1000.service/stop running (6s / 2min): (2 of 2) User job slowstop2.service/stop running (6s / 1min 30s)...
[***   ] Job user@1000.service/stop running (8s / 2min): (1 of 2) User job slowstop.service/stop running (7s / 1min 30s)...
[***   ] Job user@1000.service/stop running (10s / 2min): (2 of 2) User job slowstop2.service/stop running (9s / 1min 30s)...
[  *** ] Job user@1000.service/stop running (11s / 2min): (1 of 2) User job slowstop.service/stop running (10s / 1min 30s)...
[     *] Job user@1000.service/stop running (12s / 2min): (2 of 2) User job slowstop2.service/stop running (12s / 1min 30s)...
[   ***] Job user@1000.service/stop running (13s / 2min): (1 of 2) User job slowstop.service/stop running (13s / 1min 30s)...
[***   ] Job user@1000.service/stop running (15s / 2min): (2 of 2) User job slowstop2.service/stop running (14s / 1min 30s)...
[*     ] Job user@1000.service/stop running (15s / 2min): (2 of 2) User job slowstop2.service/stop running (14s / 1min 30s)...
[***   ] Job user@1000.service/stop running (16s / 2min): User job slowstop.service/stop running (16s / 1min 30s)...
[   ***] Job user@1000.service/stop running (18s / 2min): User job slowstop.service/stop running (17s / 1min 30s)...
[     *] Job user@1000.service/stop running (19s / 2min): User job slowstop.service/stop running (18s / 1min 30s)...
[   ***] Job user@1000.service/stop running (20s / 2min): User job slowstop.service/stop running (19s / 1min 30s)...
[*     ] Job user@1000.service/stop running (22s / 2min): User job slowstop.service/stop running (22s / 1min 30s)...
[**    ] Job user@1000.service/stop running (30s / 2min): User job slowstop.service/stop running (29s / 1min 30s)...
[   ***] Job user@1000.service/stop running (32s / 2min): User job slowstop.service/stop running (31s / 1min 30s)...
[     *] Job user@1000.service/stop running (33s / 2min): User job slowstop.service/stop running (32s / 1min 30s)...
[   ***] Job user@1000.service/stop running (34s / 2min): User job slowstop.service/stop running (33s / 1min 30s)...
[**    ] Job user@1000.service/stop running (37s / 2min): User job slowstop.service/stop running (36s / 1min 30s)...
[  *** ] Job user@1000.service/stop running (41s / 2min): User job slowstop.service/stop running (41s / 1min 30s)...
[  OK  ] Stopped user@1000.service - User Manager for UID 1000.
         Stopping user-runtime-dir@1000.service - User Runtime Directory /run/user/1000...
[  OK  ] Unmounted run-user-1000.mount - /run/user/1000.
[  OK  ] Stopped user-runtime-dir@1000.service - User Runtime Directory /run/user/1000.

If the output width is lower than approximately 100 columns, the output stops
being very useful. No idea what to do about that.