Fail when devicemapper doesn't support udev-sync

Now what we provide dynamic binaries for all plaforms,
we shouldn't try to run docker without udev sync support.

This change changes the previous warning to an Error,
unless the user explicitly overrides the warning, in
which case they're at their own risk.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/graphdriver/devmapper/deviceset.go

@@ -1621,7 +1621,10 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {
 
 	// https://github.com/docker/docker/issues/4036
 	if supported := devicemapper.UdevSetSyncSupport(true); !supported {
-		logrus.Warn("devmapper: Udev sync is not supported. This will lead to unexpected behavior, data loss and errors. For more information, see https://docs.docker.com/reference/commandline/daemon/#daemon-storage-driver-option")
+		logrus.Errorf("devmapper: Udev sync is not supported. This will lead to data loss and unexpected behavior. Install a dynamic binary to use devicemapper or select a different storage driver. For more information, see https://docs.docker.com/engine/reference/commandline/daemon/#daemon-storage-driver-option")
+		if !devices.overrideUdevSyncCheck {
+			return graphdriver.ErrNotSupported
+		}
 	}
 
 	//create the root dir of the devmapper driver ownership to match this