Add helpers to create errdef errors

Instead of having to create a bunch of custom error types that are doing
nothing but wrapping another error in sub-packages, use a common helper
to create errors of the requested type.

e.g. instead of re-implementing this over and over:

```go
type notFoundError struct {
  cause error
}

func(e notFoundError) Error() string {
  return e.cause.Error()
}

func(e notFoundError) NotFound() {}

func(e notFoundError) Cause() error {
  return e.cause
}
```

Packages can instead just do:

```
  errdefs.NotFound(err)
```

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/registry/service.go b/registry/service.go
index f3f1b4a567..ac240f0c69 100644
--- a/registry/service.go
+++ b/registry/service.go
@@ -11,6 +11,7 @@ import (
 
 	"github.com/docker/distribution/reference"
 	"github.com/docker/distribution/registry/client/auth"
+	"github.com/docker/docker/api/errdefs"
 	"github.com/docker/docker/api/types"
 	registrytypes "github.com/docker/docker/api/types/registry"
 	"github.com/pkg/errors"
@@ -117,12 +118,12 @@ func (s *DefaultService) Auth(ctx context.Context, authConfig *types.AuthConfig,
 	}
 	u, err := url.Parse(serverAddress)
 	if err != nil {
-		return "", "", validationError{errors.Errorf("unable to parse server address: %v", err)}
+		return "", "", errdefs.InvalidParameter(errors.Errorf("unable to parse server address: %v", err))
 	}
 
 	endpoints, err := s.LookupPushEndpoints(u.Host)
 	if err != nil {
-		return "", "", validationError{err}
+		return "", "", errdefs.InvalidParameter(err)
 	}
 
 	for _, endpoint := range endpoints {