Make sure we have a clean state in th test

Issue-Id: #1

tests/stests/workloads/update_workload.robot

@@ -29,7 +29,8 @@ Test Ankaios CLI update workload
     ...            AND             Set Global Variable    ${default_state_yaml_file}    ${CONFIGS_DIR}/default.yaml
     ...            AND             Set Global Variable    ${new_state_yaml_file}    %{ANKAIOS_TEMP}/itest_update_workload_new_state.yaml
     # Preconditions
-    Given Ankaios server is started with "ank-server --startup-config ${default_state_yaml_file}"
+    Given Podman has deleted all existing containers
+    And Ankaios server is started with "ank-server --startup-config ${default_state_yaml_file}"
     And Ankaios agent is started with "ank-agent --name agent_A"
     And all workloads of agent "agent_A" have an initial execution state
     And the command "curl localhost:8081" finished with exit code "0"