Show max running jobs on /tests page

[perlpunk]

See individual commits

I think we could also show the actual limit value, e.g. x jobs are running (limited by server config: 250)
WDYT?

[perlpunk]

I think we could also show the actual limit value, e.g. x jobs are running (limited by server config: 250) WDYT?

Oh wait, since this is only shown when the limit is reached I think this is redundant :)

[Martchus]

I'm fine with printing just "… (limited by server config)" in case the limit is effected. Otherwise it would be rather redundant. I'd also avoid a "x / y" format unless we are really sure not to end up with e.g. "201 / 200" in production (which would look rather buggy).

[codecov]

Codecov Report

Merging #5279 (5707d4e) into master (75a911b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #5279   +/-   ##
=======================================
  Coverage   98.31%   98.31%           
=======================================
  Files         389      389           
  Lines       37184    37190    +6     
=======================================
+ Hits        36558    36564    +6     
  Misses        626      626           

Files Changed	Coverage Δ
lib/OpenQA/Setup.pm	100.00% <ø> (ø)
t/config.t	100.00% <ø> (ø)
lib/OpenQA/Scheduler/Model/Jobs.pm	97.40% <100.00%> (ø)
lib/OpenQA/WebAPI/Controller/Test.pm	95.56% <100.00%> (+0.03%)	⬆️
t/ui/01-list.t	99.26% <100.00%> (+<0.01%)	⬆️

[perlpunk]

So I investigated the problem with max_running_jobs not always being set to the default value, causing warnings.
That is actually a problem of the tests, and it wouldn't happen in the productive code.
The problem is that apparently OpenQA::Setup::read_config is not always called when we create app instances in tests.

I think that's unfortunate because we have to cover for that in code by ensuring a default value in several places, although that should be done by OpenQA::Setup in just one place.
It would be good to make sure in tests we read the config and fill in defaults.

I will create a ticket because I had a quick look, and it looks to me like it's not fixable very fast.