bridge: Read dbus-daemon address from stdout
bridge: Read dbus-daemon address from stdout

This avoids the pipe setup, and also offers the GIOStream API, which
simplifies reading the address and error handling a lot.

martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit