channeldb: switch to Open/Create methods rather than New

Commit includes basic tests for Open/Create. Additionally, rather than
relying on btcwallet’s addmgr for encryption/decryption, this package
now exposes a simple crypto system interface.

channeldb/db_test.go

@@ -0,0 +1,38 @@
+package channeldb
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestOpenNotCreated(t *testing.T) {
+	if _, err := Open("path doesn't exist"); err != ErrNoExists {
+		t.Fatalf("channeldb Open should fail due to non-existant dir")
+	}
+}
+
+func TestCreateThenOpen(t *testing.T) {
+	// First, create a temporary directory to be used for the duration of
+	// this test.
+	tempDirName, err := ioutil.TempDir("", "channeldb")
+	if err != nil {
+		t.Fatalf("unable to create temp dir: %v")
+	}
+	defer os.RemoveAll(tempDirName)
+
+	// Next, create channeldb for the first time.
+	cdb, err := Create(tempDirName)
+	if err != nil {
+		t.Fatalf("unable to create channeldb: %v", err)
+	}
+	if err := cdb.Close(); err != nil {
+		t.Fatalf("unable to close channeldb: %v", err)
+	}
+
+	// Open should now succeed as the cdb was created above.
+	cdb, err = Open(tempDirName)
+	if err != nil {
+		t.Fatalf("unable to open channeldb: %v", err)
+	}
+}