manager: Move g-i-s chown to when PAM conversation started

During the PAM conversation, pam_gnome_keyring will try to unlock the login keyring. If the keyring created by gnome-initial-setup hasn't changed ownership, then gnome-initial-setup-copy-worker can't move it in place and gnome-keyring-daemon will try to create a new login keyring. This either means the keyring created in g-i-s is lost or g-k-d gets confused about a keyring that shows up after initializing but before it's received the unlock/create request.

Similarly, the systemd user session is started by pam_systemd and will trigger any number of services that might consume the config files g-i-s has created.

To ensure that files are ready before any consumers have started, chown them right when the user verifier has been requested and the PAM conversation starts.

Helps: gnome-keyring#137