Allow different configuration of iSCSI helper

Currently Cinder configuration hard-codes tgtadm as the only
iSCSI management utility. tgtd and tgtadm are older tools to
manage iSCSI volumes. Newer versions of Linux distros use
targetcli and kernel based iSCSI facilities (LIO) and can be
a preferred way for some users.

Change-Id: I10c0a7d596994a9201218e58ca2ad184774a8ce2
Closes-Bug: #1684139

ansible/roles/cinder/defaults/main.yml

@@ -132,7 +132,7 @@ cinder_backends:
     enabled: "{{ enable_cinder_backend_hnas_nfs | bool }}"
 
 cinder_enabled_backends: "{{ cinder_backends|selectattr('enabled', 'equalto', true)|list }}"
-
+cinder_iscsi_helper: "tgtadm"
 
 #############################################
 # Hitachi NAS Platform iSCSI and NFS drivers

ansible/roles/cinder/templates/cinder.conf.j2

@@ -96,7 +96,7 @@ lock_path = /var/lib/cinder/tmp
 volume_group = {{ cinder_volume_group }}
 volume_driver = cinder.volume.drivers.lvm.LVMVolumeDriver
 volume_backend_name = lvm-1
-iscsi_helper = tgtadm
+iscsi_helper = {{ cinder_iscsi_helper }}
 iscsi_protocol = iscsi
 {% endif %}