Add new HostConfig field, Mounts.

`Mounts` allows users to specify in a much safer way the volumes they
want to use in the container.
This replaces `Binds` and `Volumes`, which both still exist, but
`Mounts` and `Binds`/`Volumes` are exclussive.
The CLI will continue to use `Binds` and `Volumes` due to concerns with
parsing the volume specs on the client side and cross-platform support
(for now).

The new API follows exactly the services mount API.

Example usage of `Mounts`:

```
$ curl -XPOST localhost:2375/containers/create -d '{
  "Image": "alpine:latest",
  "HostConfig": {
    "Mounts": [{
      "Type": "Volume",
      "Target": "/foo"
      },{
      "Type": "bind",
      "Source": "/var/run/docker.sock",
      "Target": "/var/run/docker.sock",
      },{
      "Type": "volume",
      "Name": "important_data",
      "Target": "/var/data",
      "ReadOnly": true,
      "VolumeOptions": {
	"DriverConfig": {
	  Name: "awesomeStorage",
	  Options: {"size": "10m"},
	  Labels: {"some":"label"}
	}
      }]
    }
}'
```

There are currently 2 types of mounts:

  - **bind**: Paths on the host that get mounted into the
    container. Paths must exist prior to creating the container.
  - **volume**: Volumes that persist after the
    container is removed.

Not all fields are available in each type, and validation is done to
ensure these fields aren't mixed up between types.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

volume/volume_copy.go

@@ -2,11 +2,6 @@ package volume
 
 import "strings"
 
-const (
-	// DefaultCopyMode is the copy mode used by default for normal/named volumes
-	DefaultCopyMode = true
-)
-
 // {<copy mode>=isEnabled}
 var copyModes = map[string]bool{
 	"nocopy": false,