maint: improve VIR_ERR_INVALID_STREAM usage
    
    For streams validation, we weren't consistent on whether to
    use VIR_FROM_NONE or VIR_FROM_STREAMS.  Furthermore, in many
    API, we want to ensure that a stream is tied to the same
    connection as the other object we are operating on; while
    other API failed to validate the stream at all.  And the
    difference between VIR_IS_STREAM and VIR_IS_CONNECTED_STREAM
    is moot; as in commit 6e130ddc, we know that reference
    counting means a valid stream will always be tied to a valid
    connection.  Similar to previous patches, use a common macro
    to make it nicer.
    
    * src/datatypes.h (virCheckStreamReturn, virCheckStreamGoto):
    New macros.
    (VIR_IS_STREAM, VIR_IS_CONNECTED_STREAM): Drop unused macros.
    * src/libvirt.c: Use macro throughout.
    (virLibStreamError): Drop unused macro.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>