Remove too many inventory levels for iscsid

This fix removes unnecessary deep nesting of host groups
for iscsid service in case of Ironic hosts.
Before: iscsid -> ironic-conductor -> ironic -> control
After:  iscsid -> ironic -> control

Change-Id: Ie5393368ecbd3830f0ca01233d7b4a8ba782619a
Closes-Bug: #1716935

ansible/inventory/all-in-one

@@ -317,7 +317,7 @@ freezer
 [iscsid:children]
 compute
 storage
-ironic-conductor
+ironic
 
 [tgtd:children]
 storage

ansible/inventory/multinode

@@ -335,7 +335,7 @@ freezer
 [iscsid:children]
 compute
 storage
-ironic-conductor
+ironic
 
 [tgtd:children]
 storage