fix(manager): use valid group name when calling groupadd (#566)

Use a valid name when creating a new group with `groupadd`, as numbers
are not valid group names.

Closes #561

reana_workflow_controller/workflow_run_manager.py

@@ -27,6 +27,7 @@
     REANA_RUNTIME_JOBS_KUBERNETES_NODE_LABEL,
     REANA_RUNTIME_KUBERNETES_SERVICEACCOUNT_NAME,
     REANA_STORAGE_BACKEND,
+    WORKFLOW_RUNTIME_GROUP_NAME,
     WORKFLOW_RUNTIME_USER_GID,
     WORKFLOW_RUNTIME_USER_NAME,
     WORKFLOW_RUNTIME_USER_UID,
@@ -700,8 +701,8 @@ def _create_job_controller_startup_cmd(self, user=None):
         """Create job controller startup cmd."""
         base_cmd = "exec flask run -h 0.0.0.0;"
         if user:
-            add_group_cmd = "groupadd -f -g {} {};".format(
-                WORKFLOW_RUNTIME_USER_GID, WORKFLOW_RUNTIME_USER_GID
+            add_group_cmd = "getent group '{gid}' || groupadd -f -g '{gid}' '{name}';".format(
+                gid=WORKFLOW_RUNTIME_USER_GID, name=WORKFLOW_RUNTIME_GROUP_NAME
             )
             add_user_cmd = "useradd -u {} -g {} -M {};".format(
                 WORKFLOW_RUNTIME_USER_UID, WORKFLOW_RUNTIME_USER_GID, user