cleanup example config file + Squashed commit of the following:

commit c36b66dc952dfff91043ecbca56cf3f1f8f00703
Merge: 240d7bf f4cf934
Author: Michael DeHaan <michael@ansibleworks.com>
Date:   Tue Jun 18 13:04:51 2013 -0400

    Merge branch 'unevaluated-vars' of git://github.com/lorin/ansible into lorin_undefined

    Conflicts:
    	lib/ansible/runner/__init__.py

commit f4cf93436767f73b62a16067ab5e628830045896
Merge: 2531440 07a1365
Author: Lorin Hochstein <lorin@nimbisservices.com>
Date:   Thu Jun 6 11:07:41 2013 -0400

    Merge branch 'devel' into unevaluated-vars

commit 253144045cbafd7d72836f1017c62ac4ba623186
Author: Lorin Hochstein <lorin@nimbisservices.com>
Date:   Thu Jun 6 11:06:37 2013 -0400

    Fail template from file on undefined vars

    If config option is set, raise an exception if templating from a
    file and a variable is undefined.

commit aecb71d8b75257f0f3e11a9b176fc3737aecef8d
Author: Lorin Hochstein <lorin@nimbisservices.com>
Date:   Wed Jun 5 17:12:12 2013 -0400

    Add fail_on_undefined flag

    Add a fail_on_undefined flag to the template and template_from_string methods.

    If this flag is true, then re-raise the ninja2.excpetions.UndefinedError instead of
    swallowing it.

commit cbb1808f0585f01536240aee05a1bfd06c4b4647
Merge: d4bbf49 41425fb
Author: Lorin Hochstein <lorin@nimbisservices.com>
Date:   Wed Jun 5 16:14:12 2013 -0400

    Merge branch 'devel' into unevaluated-vars

commit d4bbf492b0b63c789d66ab60d0ec634d100fca82
Author: Lorin Hochstein <lorin@nimbisservices.com>
Date:   Mon Jun 3 19:46:13 2013 -0400

    template: Raise UndefinedError exception

    In template_from_string, raise an undefined error if it occurs.

    Have the caller catch it and throw an AnsibleUndefinedVariable

commit c94780280515f1f3756fdc429b2b1e87b365e9b7
Merge: 8d919d6 be33bcf
Author: Lorin Hochstein <lorin@nimbisservices.com>
Date:   Mon Jun 3 10:09:43 2013 -0400

    Merge branch 'devel' into unevaluated-vars

commit 8d919d6c97b28a42f47ca7248c542695baf6175f
Merge: 0f68ad8 b8630d2
Author: Lorin Hochstein <lorin@nimbisservices.com>
Date:   Thu May 30 16:27:48 2013 -0400

    Merge branch 'devel' into unevaluated-vars

commit 0f68ad8193ac17488e339a258f8c63fdae399c26
Author: Lorin Hochstein <lorin@nimbisservices.com>
Date:   Thu May 30 14:32:03 2013 -0400

    Optionally fail task on undefined variables

    This patch introduces a new configuration option called
    error_on_undefined_vars, which defaults to false.

    If this option is set to true, then a task which has unevaluated
    variables in its arguments will fail instead of running. Output looks
    like this:

        TASK: [set rabbitmq password] *************************************************
        fatal: [10.20.0.7] => Undefined variables: rabbitmq_user, rabbitmq_password
Tweak error messages for undefined variables feature.
Add undefined variables feature to example config file.