dsc_lite : Minor test suite refactors

Make minor improvements to the acceptance suite in preparation for introduction of testmode_switcher in MODULES-6474 and the conversion to beaker-rspec in MODULES-6571. This is mostly about tech debt / cleanup for the sake of maintenance.

This includes:

• Move PuppetFakeResource fixtures into a new layout so that instead of dsc_puppetfakeresource/PuppetFakeResource and dsc_puppetfakeresource/PuppetFakeResource2 the files are setup like dsc_puppetfakeresource/PuppetFakeResource/1.0 and dsc_puppetfakeresource/PuppetFakeResource/2.0. This will require updating helpers and other test code
• Adding a helper to return just windows_agents to remove Windows specific confines, like https://github.com/puppetlabs/puppetlabs-acl/blob/master/spec/spec_helper_acceptance.rb#L31-L33 and incorporating it into existing tests
• Remove the puppet_apply_debug_dsc_manifest, potentially add debug output to the puppet_apply_dsc_manifest to check for some basic emittance of powershell debug
• Remove alternate_path_separator test
• Rename uninstall_fake_reboot_resource / install_fake_reboot_resource to something more meaningful given these test fixtures are used in every test as general purpose fixtures