VOL-1460 Updated core to use voltha-protos instead of local protos
Moved protos to python directory in order to maintain functionaly of containers built there.
Added capability to do local builds of protos
Added instructions on running dep ensure for getting protos.
Updated github.com/golang/protobuf version to v1.3.1

Change-Id: Ia6ef55f07f0d5dcb5b750d7c37b21b71db85bfc4
diff --git a/vendor/github.com/golang/protobuf/protoc-gen-go/grpc/grpc.go b/vendor/github.com/golang/protobuf/protoc-gen-go/grpc/grpc.go
index faef1ab..1ddfe83 100644
--- a/vendor/github.com/golang/protobuf/protoc-gen-go/grpc/grpc.go
+++ b/vendor/github.com/golang/protobuf/protoc-gen-go/grpc/grpc.go
@@ -36,7 +36,6 @@
 
 import (
 	"fmt"
-	"path"
 	"strconv"
 	"strings"
 
@@ -53,7 +52,7 @@
 // Paths for packages used by code generated in this file,
 // relative to the import_prefix of the generator.Generator.
 const (
-	contextPkgPath = "golang.org/x/net/context"
+	contextPkgPath = "context"
 	grpcPkgPath    = "google.golang.org/grpc"
 )
 
@@ -83,8 +82,6 @@
 // Init initializes the plugin.
 func (g *grpc) Init(gen *generator.Generator) {
 	g.gen = gen
-	contextPkg = generator.RegisterUniquePackageName("context", nil)
-	grpcPkg = generator.RegisterUniquePackageName("grpc", nil)
 }
 
 // Given a type name defined in a .proto, return its object.
@@ -108,6 +105,9 @@
 		return
 	}
 
+	contextPkg = string(g.gen.AddImport(contextPkgPath))
+	grpcPkg = string(g.gen.AddImport(grpcPkgPath))
+
 	g.P("// Reference imports to suppress errors if they are not otherwise used.")
 	g.P("var _ ", contextPkg, ".Context")
 	g.P("var _ ", grpcPkg, ".ClientConn")
@@ -126,14 +126,6 @@
 
 // GenerateImports generates the import declaration for this file.
 func (g *grpc) GenerateImports(file *generator.FileDescriptor) {
-	if len(file.FileDescriptorProto.Service) == 0 {
-		return
-	}
-	g.P("import (")
-	g.P(contextPkg, " ", generator.GoImportPath(path.Join(string(g.gen.ImportPrefix), contextPkgPath)))
-	g.P(grpcPkg, " ", generator.GoImportPath(path.Join(string(g.gen.ImportPrefix), grpcPkgPath)))
-	g.P(")")
-	g.P()
 }
 
 // reservedClientName records whether a client name is reserved on the client side.