When providing and inventory layout without host_groups, linch-pin fails about linchpin

[herlo]

Sorry for the noise, if any. The <code></code> block doesn't seem to work when writing issues like it does elsewhere in markdown.

[samvarankashyap]

@herlo : the less verbose version of layout ie.,

---
inventory_layout:
  hosts:
    - openshift-ansible

because , according to the layout predefined hosts is a dictionary. Apparently , when mentioned as above the data structure of hosts changes to list.
if we would like to mention a host without its parameters , then the layout would be as follows:

---
inventory_layout:
  vars:
    openshift_hostname: __IP__
    openshift_public_hostname: __IP__
  hosts:
    openshift-master:
      count: 1
      host_groups:
        - masters
        - nodes
        - OSEv3
    openshift-repo-host:
      count: 1
      host_groups:
        - nodes
        - OSEv3
        - repo_host
    testhost1:
    testhost2:

In above layout , testhost1, testhost2 keys are associated with null.

However, commit has been made to handle the host with a all group ,

inventory_layout:
  hosts:
    openshift-ansible:
      host_groups:
        - all

[herlo]

I didn't put the layout with just a list because handling that requires extra code.

If you weren't assuming a count of 1 for each host, that was implied, but maybe not stated verbosely. Thanks for clarifying that detail. :-)

As for adding hosts without params, associating them with null seems acceptable to me. Maybe just requiring count: 1 in that case could accommodate everything? Not sure that's even necessary as long as we process it properly.

[samvarankashyap]

PR #62 addresses the above issue