Fix handler and systemd activation errors

On panic from handler: log warning and stack trace, report
InternalServerError to client

When using `podman system service` make determining the listening endpoint deterministic.

  // When determining _*THE*_ listening endpoint --
  // 1) User input wins always
  // 2) systemd socket activation
  // 3) rootless honors XDG_RUNTIME_DIR
  // 4) if varlink -- adapter.DefaultVarlinkAddress
  // 5) lastly adapter.DefaultAPIAddress

Fixes #5150
Fixes #5151

Signed-off-by: Jhon Honce <jhonce@redhat.com>

pkg/api/server/register_plugins.go

@@ -5,7 +5,7 @@ import (
 	"github.com/gorilla/mux"
 )
 
-func (s *APIServer) RegisterPluginsHandlers(r *mux.Router) error {
-	r.Handle(VersionedPath("/plugins"), APIHandler(s.Context, handlers.UnsupportedHandler))
+func (s *APIServer) registerPluginsHandlers(r *mux.Router) error {
+	r.Handle(VersionedPath("/plugins"), s.APIHandler(handlers.UnsupportedHandler))
 	return nil
 }