(PUP-1413) Add 'touch' command to Augeas provider

The touch command works like its POSIX namesake, only creating the node in
the Augeas tree when it doesn't already exist, and creating it with a NULL
value.  The behaviour is copied from augtool (augrun).
(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
(maint) Enable rubocop checking for shadowed variables

Previously, we allowed variables to be shadowed by variables
of the same name at local scope. This can make for confusing
reading to someone new to the code (and can potentially indicate
logic errors).

So this commit enables rubocop checking for shadow variables. It
also fixes (by renaming) all extant shadowed variables. Naming
is hard, but a best effort was made.
Merge pull request #3377 from domcleal/tickets/master/pup-1413-augeas-touch

(PUP-1413) Add 'touch' command to Augeas provider
Merge remote-tracking branch 'upstream/pr/3427'

* upstream/pr/3427:
  (maint) Enable rubocop checking for shadowed variables