Sync in latest go-plugin

vendor/github.com/hashicorp/go-plugin/server.go

@@ -66,6 +66,10 @@ type ServeConfig struct {
 	// the gRPC health checking service. This is not optional since go-plugin
 	// relies on this to implement Ping().
 	GRPCServer func([]grpc.ServerOption) *grpc.Server
+
+	// Logger is used to pass a logger into the server. If none is provided the
+	// server will create a default logger.
+	Logger hclog.Logger
 }
 
 // Protocol returns the protocol that this server should speak.
@@ -106,12 +110,15 @@ func Serve(opts *ServeConfig) {
 	// Logging goes to the original stderr
 	log.SetOutput(os.Stderr)
 
+	logger := opts.Logger
+	if logger == nil {
 		// internal logger to os.Stderr
-	logger := hclog.New(&hclog.LoggerOptions{
+		logger = hclog.New(&hclog.LoggerOptions{
 			Level:      hclog.Trace,
 			Output:     os.Stderr,
 			JSONFormat: true,
 		})
+	}
 
 	// Create our new stdout, stderr files. These will override our built-in
 	// stdout/stderr so that it works across the stream boundary.

vendor/vendor.json

@@ -1021,10 +1021,10 @@
 			"revisionTime": "2017-06-22T06:09:55Z"
 		},
 		{
-			"checksumSHA1": "tFCvjFzOo0x4P2SEzj8UazxTMug=",
+			"checksumSHA1": "QSH/KjHRLljyZDXMmkd9fdqbr3I=",
 			"path": "github.com/hashicorp/go-plugin",
-			"revision": "e2fbc6864d18d3c37b6cde4297ec9fca266d28f1",
-			"revisionTime": "2017-10-29T21:44:25Z"
+			"revision": "e37881a3f1a07fce82b3d99ce0342a72e53386bc",
+			"revisionTime": "2018-01-11T18:21:30Z"
 		},
 		{
 			"checksumSHA1": "yzoWV7yrS/TvOrKy5ZrdUjsYaOA=",