Split out selinux management

Currently if you have selinux enabled on the undercloud but disable it
for the overcloud, selinux is disabled on the undercloud during the
deployment. This can be resolved by only managing the selinux setting
for the deployment target hosts rather than the all.

Change-Id: I94b81ea0b954cdba7704720a145b752fa58d4308
Closes-Bug: #1874828
(cherry picked from commit 07106c501e)

common/deploy-steps.j2

@@ -436,8 +436,8 @@ outputs:
                 deploy_source_host: "DEPLOY_SOURCE_HOST"
                 deploy_target_host: "DEPLOY_TARGET_HOST"
 
-            - hosts: all
-              name: Manage SELinux and generate /etc/hosts
+            - hosts: DEPLOY_TARGET_HOST
+              name: Manage SELinux
               gather_facts: "{% raw %}{{ gather_facts | default(false) }}{% endraw %}"
               any_errors_fatal: yes
               tasks:
@@ -445,6 +445,12 @@ outputs:
                   selinux:
                     policy: targeted
                     state: SELINUX_MODE
+
+            - hosts: all
+              name: Generate /etc/hosts
+              gather_facts: "{% raw %}{{ gather_facts | default(false) }}{% endraw %}"
+              any_errors_fatal: yes
+              tasks:
 {% raw %}
                 - name: Configure Hosts Entries
                   include_role: