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/pkg/cache/shard_test.go

@@ -0,0 +1,60 @@
+package cache
+
+import "testing"
+
+func TestShardAddAndGet(t *testing.T) {
+	s := newShard(4)
+	s.Add(1, 1)
+
+	if _, found := s.Get(1); !found {
+		t.Fatal("Failed to find inserted record")
+	}
+}
+
+func TestShardLen(t *testing.T) {
+	s := newShard(4)
+
+	s.Add(1, 1)
+	if l := s.Len(); l != 1 {
+		t.Fatalf("Shard size should %d, got %d", 1, l)
+	}
+
+	s.Add(1, 1)
+	if l := s.Len(); l != 1 {
+		t.Fatalf("Shard size should %d, got %d", 1, l)
+	}
+
+	s.Add(2, 2)
+	if l := s.Len(); l != 2 {
+		t.Fatalf("Shard size should %d, got %d", 2, l)
+	}
+}
+
+func TestShardEvict(t *testing.T) {
+	s := newShard(1)
+	s.Add(1, 1)
+	s.Add(2, 2)
+	// 1 should be gone
+
+	if _, found := s.Get(1); found {
+		t.Fatal("Found item that should have been evicted")
+	}
+}
+
+func TestShardLenEvict(t *testing.T) {
+	s := newShard(4)
+	s.Add(1, 1)
+	s.Add(2, 1)
+	s.Add(3, 1)
+	s.Add(4, 1)
+
+	if l := s.Len(); l != 4 {
+		t.Fatalf("Shard size should %d, got %d", 4, l)
+	}
+
+	// This should evict one element
+	s.Add(5, 1)
+	if l := s.Len(); l != 4 {
+		t.Fatalf("Shard size should %d, got %d", 4, l)
+	}
+}