[users_spec.rb] Fix test order failures

If the `authentication_spec.rb` is run before the `user_spec.rb`, it can
set the `TokenStore.token_caches` to a particular value ("sql" in
particular) that doesn't match what is required for the test (based on
the `session_store` value), and causes the tests to fail.

By clearing the `TokenStore.token_caches` value before an after each
test, we avoid this failure.

The test failures can be reproduced in the previous commit with the
following rspec command:

  $ bundle exec rspec --order defined spec/requests/authentication_spec.rb:253 spec/requests/users_spec.rb:633

spec/requests/users_spec.rb

@@ -619,8 +619,11 @@
       # Keep this outside of the loop below with the `let` providing the value
       # for the stub, otherwise it will not work as expected
       stub_settings_merge(:server => {:session_store => session_store_value})
+      TokenStore.token_caches.clear
     end
 
+    after { TokenStore.token_caches.clear }
+
     %w[cache sql memory].each do |session_store|
       let(:session_store_value) { session_store }