Use the new error package

This is the first step in converting out static strings into well-defined
error types.  This shows just a few examples of it to get a feel for how things
will look. Once we agree on the basic outline we can then work on converting
the rest of the code over.

Signed-off-by: Doug Davis <dug@us.ibm.com>

api/server/image.go

@@ -3,6 +3,7 @@ package server
 import (
 	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -335,7 +336,7 @@ func (s *Server) postBuild(version version.Version, w http.ResponseWriter, r *ht
 			return err
 		}
 		sf := streamformatter.NewJSONStreamFormatter()
-		w.Write(sf.FormatError(err))
+		w.Write(sf.FormatError(errors.New(utils.GetErrorMessage(err))))
 	}
 	return nil
 }