builder: skip name validation for docker context

Although a builder from the store cannot be created unless
it has a valid name, this is not the case for a Docker context.

We should skip name validation when checking a node from the
store and fall back to finding one from Docker context instead.

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

store/storeutil/storeutil.go

@@ -74,7 +74,7 @@ func GetCurrentInstance(txn *store.Txn, dockerCli command.Cli) (*store.NodeGroup
 func GetNodeGroup(txn *store.Txn, dockerCli command.Cli, name string) (*store.NodeGroup, error) {
 	ng, err := txn.NodeGroupByName(name)
 	if err != nil {
-		if !os.IsNotExist(errors.Cause(err)) {
+		if !os.IsNotExist(errors.Cause(err)) && !store.IsErrInvalidName(err) {
 			return nil, err
 		}
 	}