With GLib 2.59, the `test-login-auto` test fails:

  Gcr-CRITICAL **: 14:34:24.126: expected prompt property 'choice-label'
  to be "Automatically unlock this keyring whenever I\342\200\231m
  logged in", but it is instead ""

This is because, in `mock_secret_C_Initialize()` we assign two sets of
fields to the mock module, one with `CKA_G_LOGIN_COLLECTION` → `CK_TRUE`
and one with it pointing to `CK_FALSE`.

This variable is used to decide, via `is_login_keyring()`, whether to call
`setup_unlock_keyring_login()` or `setup_unlock_keyring_other()`. The
first one sets `choice-label` to the empty string. The second one is
what we want, and upgrading GLib made it flip.

The reason is the same as the previous two fixes: the mock-secret-store
expects to be able to insert items into a hash table and then iterate it
and get them out in the same order. That was never guaranteed, and now
doesn't happen.

Let's keep a parallel list which keeps track of the order things were
added. And then instead of iterating the hash table, we iterate this
list.

Closes #21