cluster/identd/ident: add IdentError

This adds a Go error type that can be used to wrap any ErrorResponse.

Change-Id: I57fbd056ac774f4e2ae3bdf85941c1010ada0656
diff --git a/cluster/identd/ident/BUILD.bazel b/cluster/identd/ident/BUILD.bazel
index 382900e..17731c2 100644
--- a/cluster/identd/ident/BUILD.bazel
+++ b/cluster/identd/ident/BUILD.bazel
@@ -4,6 +4,7 @@
     name = "go_default_library",
     srcs = [
         "client.go",
+        "errors.go",
         "request.go",
         "response.go",
         "server.go",