BaR doc update + lftp missing package

There is a ReaR option to copy files to the backup with sftp this "feature" needs the
lftp package. This patch adds the lftp package to be installed when ReaR is installed.

The documentation regarding backup-and-restore role is not update, the name of the
role uses undescores. This patch updates the name of the role on the documentation.

Change-Id: I5435780a280e9a1eecacab488de1f0e5165f430e

doc/source/roles/role-backup_and_restore.rst

@@ -1,5 +1,5 @@
 =========================
-Role - backup-and-restore
+Role - backup_and_restore
 =========================
 
 .. ansibleautoplugin::
@@ -51,7 +51,7 @@ Undercloud node.
     hosts: undercloud
     name: Setup NFS server for ReaR
     roles:
-    - role: backup-and-restore
+    - role: backup_and_restore
   EOF
 
 Then, we will create another playbook to determine the location
@@ -67,7 +67,7 @@ in which we will like to install ReaR.
     hosts: Controller
     name: Install ReaR
     roles:
-    - role: backup-and-restore
+    - role: backup_and_restore
   EOF
 
 Now we create the playbook to create the actual backup.
@@ -92,7 +92,7 @@ Now we create the playbook to create the actual backup.
     hosts: Controller
     name: Create the recovery images for the control plane
     roles:
-    - role: backup-and-restore
+    - role: backup_and_restore
   EOF
 
 The last step is to run the previously create playbooks

tripleo_ansible/roles/backup_and_restore/vars/redhat.yml

@@ -26,5 +26,6 @@ tripleo_backup_and_restore_rear_packages:
   - syslinux
   - genisoimage
   - nfs-utils
+  - lftp
 tripleo_backup_and_restore_nfs_packages:
   - nfs-utils