global: move to context (#1699)

* global: move to context

Move from golang.org/x/net/context to std lib's context.

Change done with:

for i in $(grep -l '/context' **/*.go); do sed -e 's|golang.org/x/net/context|context|' -i $i; echo $i; done
for i in **/*.go; do goimports -w $i; done

* drop from dns.pb.go as well

core/dnsserver/server.go

@@ -2,6 +2,7 @@
 package dnsserver
 
 import (
+	"context"
 	"fmt"
 	"net"
 	"runtime"
@@ -18,7 +19,6 @@ import (
 
 	"github.com/miekg/dns"
 	ot "github.com/opentracing/opentracing-go"
-	"golang.org/x/net/context"
 )
 
 // Server represents an instance of a server, which serves

core/dnsserver/server_grpc.go

@@ -1,6 +1,7 @@
 package dnsserver
 
 import (
+	"context"
 	"crypto/tls"
 	"errors"
 	"fmt"
@@ -9,7 +10,6 @@ import (
 	"github.com/grpc-ecosystem/grpc-opentracing/go/otgrpc"
 	"github.com/miekg/dns"
 	"github.com/opentracing/opentracing-go"
-	"golang.org/x/net/context"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/peer"
 

core/dnsserver/server_test.go

@@ -1,13 +1,13 @@
 package dnsserver
 
 import (
+	"context"
 	"testing"
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/test"
 
 	"github.com/miekg/dns"
-	"golang.org/x/net/context"
 )
 
 type testPlugin struct{}

core/dnsserver/server_tls.go

@@ -1,12 +1,12 @@
 package dnsserver
 
 import (
+	"context"
 	"crypto/tls"
 	"fmt"
 	"net"
 
 	"github.com/miekg/dns"
-	"golang.org/x/net/context"
 )
 
 // ServerTLS represents an instance of a TLS-over-DNS-server.