kvdb: unify how the db backend for tests is set

kvdb/kvdb_etcd.go

@@ -7,9 +7,9 @@ import (
 	"github.com/lightningnetwork/lnd/kvdb/etcd"
 )
 
-// TestBackend is conditionally set to etcd when the kvdb_etcd build tag is
+// EtcdBackend is conditionally set to etcd when the kvdb_etcd build tag is
 // defined, allowing testing our database code with etcd backend.
-const TestBackend = EtcdBackendName
+const EtcdBackend = true
 
 // GetEtcdTestBackend creates an embedded etcd backend for testing
 // storig the database at the passed path.