keyring: open session when getting secret service

Or we'll fail the call to secret_service_encode_dbus_secret().

https://bugzilla.gnome.org/show_bug.cgi?id=733421
keyring: fix variant syntax

We should pass a tuple.

https://bugzilla.gnome.org/show_bug.cgi?id=733421
copy-worker: run in EarlyInitialization

The EarlyInitialization phase was added to gnome-session for the purpose
of running components that need to complete before the Initialization
phase (where e.g. the keyring gets started).
Use it for the initial setup copy worker.

https://bugzilla.gnome.org/show_bug.cgi?id=733421
keyring: report error when failing to change keyring password

Helps with debugging.

https://bugzilla.gnome.org/show_bug.cgi?id=733421
keyring: use correct object path

Or we'll fail the DBus call.

https://bugzilla.gnome.org/show_bug.cgi?id=733421