Repair software release tests

* [slapos-master](https://nexedijs.erp5.net/#/test_result_module/20210629-DE509CB3/23) is failing in checkSoftware step, because:
  * wcfs is linked against system zlib (fixed in this MR)
  * the .so in the build directory have missing references. I think we don't need to check in build folders and also liblibgolang is missing, but it's not a problem because of the way we load dynamically at runtime, so I suggest changing checkSoftware in slapos.core!317
* [gitlab](https://nexedijs.erp5.net/#/test_result_module/20210629-DE509CB3/10) is failing for some time because mimemagic have been yanked from rubygems. This is a minimal change to get the test running again, to prevent other problems to sneak in while we don't have tests

See merge request !1007
23 jobs for feat/seleniumserver-new-browsers in 0 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

passed SlapOS.SlapRunner.ResilienceTest-Master

00:22:22

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

06:20:27

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

03:36:12

passed SlapOS.Eggs.UnitTest-Master.Python2

00:10:17

passed SlapOS.Eggs.UnitTest-Master.Python2

00:11:16

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python2

00:14:39

passed SlapOS.Eggs.UnitTest-Master.Python2

00:07:59

passed SlapOS.Eggs.UnitTest-Master.Python2

00:14:27

passed SlapOS.Eggs.UnitTest-Master.Python3

00:16:27

passed SlapOS.Eggs.UnitTest-Master.Python3

passed SlapOS.Eggs.UnitTest-Master.Python3

00:00:05

passed SlapOS.Eggs.UnitTest-Master.Python3

00:58:42

passed SlapOS.Eggs.UnitTest-Master.Python3

00:11:32

passed SlapOS.Eggs.UnitTest-Master.Python3

passed SlapOS.Eggs.UnitTest-Master.Python3

00:13:01

passed SlapOS.SlapRunner.ResilienceTest-Master

00:22:07

passed SlapOS.SlapRunner.ResilienceTest-Master

00:22:28

passed SlapOS.SlapRunner.ResilienceTest-Master

00:22:32

passed SlapOS.SlapRunner.ResilienceTest-Master