Configure dracut multipath module for diskless nodes

Configure dracut multipath module for diskless nodes in order to
allow initramfs to load multipath module in order to allow bootable
device to be multipathed.

Change-Id: If346b7fcb2362a7454652a22d4a1f96f7f5e9dca

tripleo_ansible/roles/tripleo_multipathd/defaults/main.yml

@@ -24,3 +24,4 @@ tripleo_multipathd_enable: true
 tripleo_multipathd_find_multipaths: true
 tripleo_multipathd_skip_kpartx: true
 tripleo_multipathd_user_friendly_names: false
+tripleo_boot_from_multipath_device: false

tripleo_ansible/roles/tripleo_multipathd/tasks/host_prep.yml

@@ -67,3 +67,26 @@
     path: /etc/multipath
     state: directory
     setype: container_file_t
+
+- name: Configure multipath dracut module
+  when:
+    - tripleo_boot_from_multipath_device | bool
+  block:
+    - name: Check if multipath module is already configured in dracut
+      lineinfile:
+        state: absent
+        path: "/etc/dracut.conf"
+        regexp: "add_dracutmodules.*multipath.*"
+      check_mode: true
+      changed_when: false
+      register: check
+    - name: Add multipath dracut module if it's missing and refresh dracut
+      when: check.found == 0
+      block:
+        - name: Add multipath dracut module if it's missing
+          lineinfile:
+            state: present
+            path: "/etc/dracut.conf"
+            line: 'add_dracutmodules+="multipath"'
+        - name: Refresh dracut
+          shell: dracut -f