Allow the Transport class to be used for non-master nodes

Allow the Transport class to be used for non-master nodes

If a communication failure occurred and the caller was not running on
the master node, Transport assumed that this itself was the cause of
the error condition.

However, for communication with the metadata daemon we need to support
non-master nodes as well.

Add a parameter that allows to use the class on non-master nodes.

Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>