Role should fail immediately when its preconditions are not met

While we were failing before, that failure occurs mid-way through
the execution of the role. If we are going to fail, let's fail as
fast as possible.

Change-Id: I97bf2934042fc7ebe7f688f1f21a3cc4360ff61d

tasks/galera_install.yml

@@ -13,13 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-- name: Fail if the galera root password is not provided
-  fail:
-    msg: |
-      Please set the galera_root_password variable prior to applying the
-      galera role.
-  when: (galera_root_password is undefined) or (galera_root_password is none)
-
 - name: Preseed galera password(s)
   debconf:
     name: "{{ item.name }}"

tasks/main.yml

@@ -13,6 +13,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+- name: Fail if the galera root password is not provided
+  fail:
+    msg: |
+      Please set the galera_root_password variable prior to applying the
+      galera role.
+  when: (galera_root_password is undefined) or (galera_root_password is none)
+
 - include: galera_upgrade_check.yml
 - include: galera_cluster_state.yml
 - include: galera_pre_install.yml