(#16178) Handle the case where temp_answer is false but defined.

Consider:

````
  class foomodule::params {
    $myitem = false
    ...
````

The current code won't handle this because `if temp_answer` is the same
as `if false`.

This commit changes it to use `temp_anser.nil?` instead.
(#16178) Add test for behavior of false values in lookup

This adds a test around the fix to treat a false value in a hierarchy as
a real value.
(Maint) Require Hiera::Backend where it is used

Previously the Hiera::Backend::Puppet_backend code assumed that
Hiera::Backend had already been included. This was not true, at least in
the tests. This commit has the backend require the files that it expects
to already be loaded for it to work correctly.
(Maint) Remove duplication and mocking from tests

The tests used to have a large amount of duplication around setting
configuration values for Hiera, this extracts them into a common spot
and also removes some of the mocking that was being done in order to
make the tests a little more straightforward and less tied to the
implementation.
(#16178) Stop checking for :undefined

Puppet no longer returns :undefined as a special value from variable
lookups. This commit removes this extra check from the Hiera puppet
backend.
(Maint) Test interplay of colliding names

This adds tests to ensure that the way scope is handled in the case of a
variable name colliding with a class name is nailed down. It also adds a
case to call out that nodescope is different from topscope.
Merge branch 'maint/master/more-scoping-examples'

* maint/master/more-scoping-examples:
  (Maint) Test interplay of colliding names
Merge pull request #1282 from zaphod42/issue/3.0.x/16178-hiera-puppet-backend-does-not-handle-false

(#16178) Handle the case where the value found is false
(Maint) Stop changing internals of object during test

Previously the test depended on the internal implementation of
CommandLine (specifically the @args instance var) to control the test.
This makes the test very brittle. This changes it to use the public
interface of CommandLine.
(#7316) Use the public API for initializing settings

Previously the Puppet::Util::CommandLine code would use unpublished APIs
for initializing the application. Although this worked, it caused at
least two problems.
  1) The command line code was tied to the internals of puppet
  2) The public API could not actually be used for achieving what the
  command line code did

This commit changes the Puppet::Util::CommandLine class to start using
the public API of Puppet.initialize_settings for initializing puppet.
This required adding a new parameter to initialize_settings so that the
command line arguments could be passed in. It also required removing the
restriction that application_defaults can only be initialized once,
since the public behavior of the initialize_settings method is to
initialize both global and application settings at once.
(#7316) Load puppet/util as early as possible

Previously the puppet/util code was only loaded after the system had
been running. This pattern of loading has sometimes lead to bad
dependency cycles that have gone undetected. This moves the loading to
be earlier so that we can catch those kinds of problems if they come up.
(#7316) Do not try to require the application

The previous behavior of the CommandLine trying to load the application
is unneeded and duplicates what the Puppet::Application.find method
does. There is no need to do it. This commit removes CommandLine trying
to require the application.
(Maint) Remove distracting comments

The comments did nothing to elucidate the code. Removing them puts the
code closer together and easier to follow.
(#7316) Reorder subcommand handling logic

The previous logic for handling subcommands was a mixture of negation
and unless which made it hard to follow. This untangles it by nesting
the conditions in a more natural manner.
(Maint) Extract classes to handle different subcommand types

Previously the logic about how to find and execute the different kinds
of subcommands were all tied together in a single conditional structure.
This made it harder to isolate the different styles. This commit
extracts them out into individual classes for execution and a single
method to decide which execution class is needed for the given
subcommand.
(Maint) Remove unused instance variables
(#7316) Clarify parameters to construct a CommandLine

This adds documentation around the parameters that are to be passed to a
CommandLine constructor. It turns out that one of them is unused and so
the tests around it being special are removed and the documentation
states that it is unused.
(Maint) Simplify logic to find subcommand name

The previous logic around figuring out the subcommand name duplicated a
check for options and had an implicit check for an empty list of
arguments. This makes it more straightforward.
(Maint) Separate discovery of subcommand name from args

The discovery of subcommand and args was tied together. This separates
them and should make the rules around the subcommand name and the
arguments to that command a little clearer and independent of eachother.
(#7316) Document API used by CommandLine

This commit adds documentation to the methods and classes used by
CommandLine in order to bootstrap puppet, load an application, and
execute it.