Windows: Add named pipe mount support

Current insider builds of Windows have support for mounting individual
named pipe servers from the host to the guest. This allows, for example,
exposing the docker engine's named pipe to a container.

This change allows the user to request such a mount via the normal bind
mount syntax in the CLI:

  docker run -v \\.\pipe\docker_engine:\\.\pipe\docker_engine <args>

Signed-off-by: John Starks <jostarks@microsoft.com>
Upstream-commit: 54354db850664783918a1fc9d208bcfcf47c28e2
Component: engine

components/engine/api/types/mount/mount.go

@@ -15,6 +15,8 @@ const (
 	TypeVolume Type = "volume"
 	// TypeTmpfs is the type for mounting tmpfs
 	TypeTmpfs Type = "tmpfs"
+	// TypeNamedPipe is the type for mounting Windows named pipes
+	TypeNamedPipe Type = "npipe"
 )
 
 // Mount represents a mount (volume).