Volumes refactor and external plugin implementation.

Signed by all authors:

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Signed-off-by: Arnaud Porterie <arnaud.porterie@docker.com>
Signed-off-by: David Calavera <david.calavera@gmail.com>
Signed-off-by: Jeff Lindsay <progrium@gmail.com>
Signed-off-by: Alexander Morozov <lk4d4@docker.com>
Signed-off-by: Luke Marsden <luke@clusterhq.com>
Signed-off-by: David Calavera <david.calavera@gmail.com>

volume/drivers/proxy.go

@@ -0,0 +1,65 @@
+package volumedrivers
+
+// currently created by hand. generation tool would generate this like:
+// $ rpc-gen volume/drivers/api.go VolumeDriver > volume/drivers/proxy.go
+
+type volumeDriverRequest struct {
+	Name string
+}
+
+type volumeDriverResponse struct {
+	Mountpoint string `json:",ommitempty"`
+	Err        error  `json:",ommitempty"`
+}
+
+type volumeDriverProxy struct {
+	c client
+}
+
+func (pp *volumeDriverProxy) Create(name string) error {
+	args := volumeDriverRequest{name}
+	var ret volumeDriverResponse
+	err := pp.c.Call("VolumeDriver.Create", args, &ret)
+	if err != nil {
+		return err
+	}
+	return ret.Err
+}
+
+func (pp *volumeDriverProxy) Remove(name string) error {
+	args := volumeDriverRequest{name}
+	var ret volumeDriverResponse
+	err := pp.c.Call("VolumeDriver.Remove", args, &ret)
+	if err != nil {
+		return err
+	}
+	return ret.Err
+}
+
+func (pp *volumeDriverProxy) Path(name string) (string, error) {
+	args := volumeDriverRequest{name}
+	var ret volumeDriverResponse
+	if err := pp.c.Call("VolumeDriver.Path", args, &ret); err != nil {
+		return "", err
+	}
+	return ret.Mountpoint, ret.Err
+}
+
+func (pp *volumeDriverProxy) Mount(name string) (string, error) {
+	args := volumeDriverRequest{name}
+	var ret volumeDriverResponse
+	if err := pp.c.Call("VolumeDriver.Mount", args, &ret); err != nil {
+		return "", err
+	}
+	return ret.Mountpoint, ret.Err
+}
+
+func (pp *volumeDriverProxy) Unmount(name string) error {
+	args := volumeDriverRequest{name}
+	var ret volumeDriverResponse
+	err := pp.c.Call("VolumeDriver.Unmount", args, &ret)
+	if err != nil {
+		return err
+	}
+	return ret.Err
+}