Plugin client's handle plugin dying

This PR plumbs the plugins done ctx through the base and driver plugin
clients (device already had it). Further, it adds generic handling of
gRPC stream errors.

drivers/java/driver.go

@@ -1,6 +1,7 @@
 package java
 
 import (
+	"context"
 	"fmt"
 	"os"
 	"os/exec"
@@ -23,7 +24,6 @@ import (
 	"github.com/hashicorp/nomad/plugins/shared"
 	"github.com/hashicorp/nomad/plugins/shared/hclspec"
 	"github.com/hashicorp/nomad/plugins/shared/loader"
-	"golang.org/x/net/context"
 )
 
 const (