Install rally only on first utility container

Rally should be installed only on first utility container.
We do the same for tempest.

I see no reason of having that installed on all utility containers.
Additionally, because rally does not have serial ['1', '100%'],
python_venv_build may fail due to the venv_wheel_build_skip_check[1].

[1] a3b3b7d7aa/tasks/main.yml (L44)

Change-Id: Ibe79c4fbcaa40b673056b0ef95c7380f9a23f747

playbooks/os-rally-install.yml

@@ -14,13 +14,13 @@
 # limitations under the License.
 
 - name: Gather rally facts
-  hosts: utility_all
+  hosts: utility_all[0]
   gather_facts: "{{ osa_gather_facts | default(True) }}"
   tags:
     - always
 
 - name: Installation and setup of Rally
-  hosts: utility_all
+  hosts: utility_all[0]
   gather_facts: false
   user: root
   environment: "{{ deployment_environment_variables | default({}) }}"