Wall clock time for releases

The idea of this issue is to keep track of IUK build times over time, to make sure they don't go haywire:

Version	Local build	Jenkins build
4.7	real 52m55.065s user 276m40.886s sys 73m48.176s (kibi@hamburg, 4 jobs)	parallel_build_IUKs: 1h 6m collect_build_IUKs: 17m
4.9	real 73m21.990s user 441m45.229s sys 90m53.784s (kibi@hamburg, 4 jobs)	parallel_build_IUKs: 1h 32m collect_build_IUKs: 29m
4.11	real 108m10.000s user 590m1.000s sys 129m7.000s (anonym, 4 jobs over 4 cores)	parallel_build_IUKs: 1h51m parallel_collect_IUKs: 35m
4.12	useless data (lack of disk space, had to re-run)	parallel_build_IUKs: 1h56m parallel_collect_IUKs: 40m
4.13	real 114m52.830s user 642m6.442s sys 128m35.027s (anonym, 4 jobs over 4 cores)	parallel_build_IUKs: 1h56m parallel_collect_IUKs: 36m
4.14	real 216m51.291s user 1140m11.311s sys 166m17.646s (intrigeri, 2 jobs over 4 core in a VM with 8GB of RAM)	2h04m
4.15	real 204m17.481s user 1037m54.349s sys 156m33.292s (intrigeri, 2 jobs over 4 core in a VM with 8GB of RAM)	2h08m
4.15.1	real 125m59.683s user 693m9.286s sys 149m24.942s (anonym, 4 jobs over 4 cores)	2h03m
4.16	real 130m36.672s user 722m36.200s sys 149m26.397s (anonym, 4 jobs over 4 cores)	2h19m
4.17	3h06m (intrigeri, 4 jobs over 4 cores)	2h11m
4.18	3h27m (intrigeri, 4 jobs over 4 cores)	2h13m
4.19~rc1	real 224m40.289s user 1102m58.466s sys 226m28.777s (anonym, 4 jobs over 4 cores, thermal problems)	2h28m
4.19	4h03m (intrigeri, 4 jobs over 4 cores)	2h30m
4.20~rc1	real 172m27.710s user 961m22.474s sys 206m19.210s (anonym, 4 jobs over 4 cores)	2h24m
4.20	real 180m57.011s user 1000m1.650s 219m38.893s (anonym, 4 jobs over 4 cores)	2h42m
4.21	4h11m	2h59m
4.22~rc1	1h24m (boyska, 8 jobs over 8 cores)	2h47m
4.22	3h20m (anonym, 4 jobs over 4 cores)	2h52m
4.23	36059.40s user 7867.90s system 1195% cpu 1:01:14.82 total (boyska, 8 jobs over 8 cores)	4 hr 33 min (running on a single iguana isobuilder)
4.24 (squashfs-tools-ng)	8h15m (anonym, 4 jobs over 4 cores)	5h23m (1 × iguana, 2 × lizard)
4.25	5h19m (anonym, 4 jobs over 4 cores)	2h18m (iguana + lizard)
4.26	1h40m (boyska, 8 jobs over 8 cores)	2h33m (iguana + lizard)
4.27	6h51 (intrigeri, 4 jobs over 4 cores)	2h48m (iguana + lizard)
4.28	1h41m (boyska, 8 jobs over 8 cores)	2h27m (2xiguana + 4xlizard)
4.29	1h47m (boyska, 8 jobs over 8 cores)	2h54m (2xiguana + 4xlizard)
5.0	4min (boyska, 8 jobs over 8 cores)	8min (iguana)