Add support for shared ansible_host in inventory

Today it is possible to create the following ansible inventory file:

  [foo]
  foo01 ansible_host=192.168.1.1

  [bar]
  bar01 ansible_host=192.168.1.1

Which allows a user to create multiple host aliases for a single
connection. This could be done with ansible groups, however there is
some functional differences on how ansible runs in that configuration.

We could also request 2 nodes from nodepool, however in this case, it
would be a waste of CI resources because every alias would need a new
node from nodepool.

Now, a user is able to alias multiple host names to a single node from
nodepool by doing the following:

  nodeset:
    nodes:
      - name:
          - foo
          - bar
        label: ubuntu-xenial

This would result in a single node request from nodepool, but create
an inventory file with 2 alaises sharing and single ansible_host
variable.

Change-Id: I674d6baac26852ee1503feb1ed16c279bf773688
Signed-off-by: Paul Belanger <pabelanger@redhat.com>
diff --git a/doc/source/user/config.rst b/doc/source/user/config.rst
index fa874a9..edd3222 100644
--- a/doc/source/user/config.rst
+++ b/doc/source/user/config.rst
@@ -1201,7 +1201,9 @@
            label: controller-label
          - name: compute1
            label: compute-label
-         - name: compute2
+         - name:
+             - compute2
+             - web
            label: compute-label
        groups:
          - name: ceph-osd
@@ -1212,6 +1214,9 @@
              - controller
              - compute1
              - compute2
+          - name: ceph-web
+            nodes:
+              - web
 
 .. attr:: nodeset
 
@@ -1233,6 +1238,9 @@
          The name of the node.  This will appear in the Ansible inventory
          for the job.
 
+         This can also be as a list of strings. If so, then the list of hosts in
+         the Ansible inventory will share a common ansible_host address.
+
       .. attr:: label
          :required: