Don't start Geoclue providers until necessary.

Creating the Geoclue master client starts the Geoclue providers. This
causes the Geoclue provides to start, even though startUpdates() hasn't
been called yet. Defer creating the master client until startUpdates()
is called and destroy it when stopUpdates() is called.

Change-Id: I8a40eb1d68b50288742b8da088bc14904b1165ba
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>