Add example of walking through sign in to a placements system test

spec/system/placements/support/users/support_user_invites_a_new_user_spec.rb

@@ -113,8 +113,12 @@ def and_there_is_an_existing_persona_for(persona_name)
     create(:placements_support_user, persona_name.downcase.to_sym)
   end
 
-  def and_i_visit_the_personas_page
-    visit personas_path
+  def and_i_visit_root_path
+    visit placements_root_path
+  end
+
+  def and_i_click_on_sign_in
+    click_on "Sign in using a Persona"
   end
 
   def and_i_click_sign_in_as(persona_name)
@@ -123,7 +127,8 @@ def and_i_click_sign_in_as(persona_name)
 
   def given_i_am_signed_in_as_a_support_user
     and_there_is_an_existing_persona_for("Colin")
-    and_i_visit_the_personas_page
+    and_i_visit_root_path
+    and_i_click_on_sign_in
     and_i_click_sign_in_as("Colin")
   end