Adding is_atomic in centos bootstrap-os (#3873)

Adding fact is_atomic in bootstrap-centos.yml.

Fix issue: #3538

roles/bootstrap-os/tasks/bootstrap-centos.yml

 ---
+- name: check if atomic host
+  stat:
+    path: /run/ostree-booted
+  register: ostree
+
+- set_fact:
+    is_atomic: "{{ ostree.stat.exists }}"
 
 - name: Check presence of fastestmirror.conf
   stat:
@@ -30,8 +37,12 @@
     packages:
       - libselinux-python
       - epel-release
+  when:
+    - not is_atomic
 
 - name: Install pip for bootstrap
   yum:
     name: python-pip
     state: present
+  when:
+    - not is_atomic