Only build rkt driver on linux

Build stub for non-linux targets

client/driver/rkt.go

@@ -1,3 +1,5 @@
+//+build linux
+
 package driver
 
 import (
@@ -225,7 +227,7 @@ func rktManifestMakePortMap(manifest *appcschema.PodManifest, configPortMap map[
 	return portMap, nil
 }
 
-// NewRktDriver is used to create a new exec driver
+// NewRktDriver is used to create a new rkt driver
 func NewRktDriver(ctx *DriverContext) Driver {
 	return &RktDriver{DriverContext: *ctx}
 }

client/driver/rkt_nonlinux.go

@@ -0,0 +1,55 @@
+//+build !linux
+
+package driver
+
+import (
+	"time"
+
+	"github.com/hashicorp/nomad/client/config"
+	cstructs "github.com/hashicorp/nomad/client/structs"
+	"github.com/hashicorp/nomad/nomad/structs"
+)
+
+// NewRktDriver returns an unimplemented driver that returns false during
+// fingerprinting.
+func NewRktDriver(*DriverContext) Driver {
+	return RktDriver{}
+}
+
+type RktDriver struct{}
+
+func (RktDriver) Prestart(*ExecContext, *structs.Task) (*PrestartResponse, error) {
+	panic("not implemented")
+}
+
+func (RktDriver) Start(ctx *ExecContext, task *structs.Task) (*StartResponse, error) {
+	panic("not implemented")
+}
+
+func (RktDriver) Open(ctx *ExecContext, handleID string) (DriverHandle, error) {
+	panic("not implemented")
+}
+
+func (RktDriver) Cleanup(*ExecContext, *CreatedResources) error {
+	panic("not implemented")
+}
+
+func (RktDriver) Validate(map[string]interface{}) error {
+	panic("not implemented")
+}
+
+func (RktDriver) Abilities() DriverAbilities {
+	panic("not implemented")
+}
+
+func (RktDriver) FSIsolation() cstructs.FSIsolation {
+	panic("not implemented")
+}
+
+func (RktDriver) Fingerprint(cfg *config.Config, node *structs.Node) (bool, error) {
+	return false, nil
+}
+
+func (RktDriver) Periodic() (bool, time.Duration) {
+	return false, 0
+}