verror: addressing https://github.com/veyron/release-issues/issues/1080

MultiPart: 1/3
Change-Id: I190b1dd5004025dac6acfd58f59483588bf70d9d
diff --git a/lib/exec/config.go b/lib/exec/config.go
index 67427b3..f6eae2e 100644
--- a/lib/exec/config.go
+++ b/lib/exec/config.go
@@ -61,7 +61,7 @@
 	defer c.RUnlock()
 	v, ok := c.m[key]
 	if !ok {
-		return "", verror.New(verror.NoExist, nil, "config.Get", key)
+		return "", verror.New(verror.ErrNoExist, nil, "config.Get", key)
 	}
 	return v, nil
 }