software/theia/test: fix a flaky test

This test checks that running `slapos node software` command on theia
shell starts installing software, but this command might get an error
like:

    process started, but another slapos process is aleady running with pid 2656158, exiting

this happened for example with https://erp5js.nexedi.net/#/test_result_module/20240911-ED8B4BF9/60
26 jobs for fix/theia-software-test in 0 seconds
Status Job ID Name Coverage
  External
passed Cloudooo.UnitTest-Master

00:09:30

passed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

00:41:16

failed ERP5.UnitTest-Zope4Py3-Py2

07:33:30

passed SlapOS.Eggs.UnitTest-Master.Python2

00:27:28

passed SlapOS.Eggs.UnitTest-Master.Python3

00:25:03

passed SlapOS.Eggs.UnitTest-TestRunner1.Python2

00:12:22

passed SlapOS.Eggs.UnitTest-TestRunner1.Python3

00:43:50

failed SlapOS.SoftwareReleases.IntegrationTest-Master

13:43:35

failed SlapOS.SoftwareReleases.IntegrationTest-TestRunner1

11:45:32

failed SlapOS.Theia.ResilienceTest-Master-ERP5

09:47:41

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

00:36:27

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

15:02:11

passed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

00:49:49

failed ERP5.UnitTest-Zope4Py3-Py2

03:54:37

passed SlapOS.Eggs.UnitTest-Master.Python2

00:26:49

failed SlapOS.Eggs.UnitTest-Master.Python2

00:24:56

failed SlapOS.Eggs.UnitTest-Master.Python3

00:25:11

passed SlapOS.Eggs.UnitTest-Master.Python3

00:26:19

passed SlapOS.Eggs.UnitTest-TestRunner1.Python2

00:08:34

passed SlapOS.Eggs.UnitTest-TestRunner1.Python2

00:26:02

passed SlapOS.Eggs.UnitTest-TestRunner1.Python3

00:34:54

passed SlapOS.Eggs.UnitTest-TestRunner1.Python3

00:26:00

failed SlapOS.SoftwareReleases.IntegrationTest-Master

12:08:01

failed SlapOS.SoftwareReleases.IntegrationTest-TestRunner1

13:10:08

failed SlapOS.SoftwareReleases.IntegrationTest-TestRunner1

08:58:07

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

00:52:43