(PUP-3697) Default key to certname for find action

If no key is supplied to the find action to indirector based faces,
default it to the certname. This way things such as `puppet facts find`
work without inventing a key to find facts for.
(PUP-3698) Make find the default action for facts

Finding facts is by far the most common action for the facts face so it
should be the default.
(PUP-3698) Don't default to certname for the resource_type face

For this face we don't want to default to the certname like other
indirector based faces. Instead we want the user to always supply a
argument.
(PUP-3698) Update documentation for affected faces

Update the documentation for certificate_request, status and
certificate_revocation_list.

status and certificate_revocation_list no longer requires a dummy
argument.
certificate_request now defaults to find the CSR for the current node
certname.
Merge pull request #3337 from dalen/improve_facts_face

(PUP-3697, PUP-3698) Improve facts face
* (PUP-3697) Default key to certname for find action
* (PUP-3698) Make find the default action for facts
* (PUP-3698) Don't default to certname for the resource_type face
* (PUP-3698) Update documentation for affected faces