Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/test/server.go

@@ -0,0 +1,52 @@
+package test
+
+import (
+	"net"
+	"sync"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+// TCPServer starts a DNS server with a TCP listener on laddr.
+func TCPServer(laddr string) (*dns.Server, string, error) {
+	l, err := net.Listen("tcp", laddr)
+	if err != nil {
+		return nil, "", err
+	}
+
+	server := &dns.Server{Listener: l, ReadTimeout: time.Hour, WriteTimeout: time.Hour}
+
+	waitLock := sync.Mutex{}
+	waitLock.Lock()
+	server.NotifyStartedFunc = func() { waitLock.Unlock() }
+
+	go func() {
+		server.ActivateAndServe()
+		l.Close()
+	}()
+
+	waitLock.Lock()
+	return server, l.Addr().String(), nil
+}
+
+// UDPServer starts a DNS server with an UDP listener on laddr.
+func UDPServer(laddr string) (*dns.Server, string, error) {
+	pc, err := net.ListenPacket("udp", laddr)
+	if err != nil {
+		return nil, "", err
+	}
+	server := &dns.Server{PacketConn: pc, ReadTimeout: time.Hour, WriteTimeout: time.Hour}
+
+	waitLock := sync.Mutex{}
+	waitLock.Lock()
+	server.NotifyStartedFunc = func() { waitLock.Unlock() }
+
+	go func() {
+		server.ActivateAndServe()
+		pc.Close()
+	}()
+
+	waitLock.Lock()
+	return server, pc.LocalAddr().String(), nil
+}