user: Always return supplementary groups

The caller can ignore it if they don't care about using them.

Signed-off-by: Mrunal Patel <[email protected]>

libcontainer/user/user.go

@@ -417,11 +417,10 @@ func GetExecUser(userSpec string, defaults *ExecUser, passwd, group io.Reader) (
 
 				// Okay, so it's numeric. We can just roll with this.
 			}
-		} else if len(groups) > 0 {
-			// Supplementary group ids only make sense if in the implicit form.
-			user.Sgids = make([]int, len(groups))
-			for i, group := range groups {
-				user.Sgids[i] = group.Gid
+		}
+		if len(groups) > 0 {
+			for _, group := range groups {
+				user.Sgids = append(user.Sgids, group.Gid)
 			}
 		}
 	}