maint: Fix order dependent test failure

The spec tests failed when running spec/unit/face/node_spec.rb
followed by spec/unit/ssl/certificate_request_spec.rb, because the
clean action for the node face was leaving
Puppet::SSL::Host.ca_location set to :local instead of its default
:none state.

This commit resets the ca_location back to :none in the top-level
after :all block.