deploy-test/runTestSuite: fix a python3 incompatibility

NamedTemporaryFile are w+b by default.
6 jobs for feat/slapos-testing-py3 in 0 seconds
Status Job ID Name Coverage
  External
passed Cloudooo.UnitTest-Master

00:18:01

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

passed SlapOS.KVM.ResilienceTest-Master

passed SlapOS.SlapRunner.ResilienceTest-Master

00:24:26

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

01:29:53