this patch adds an non-RFC extenstion to the redirect login response which allows
a target to temporarily redirect not only to a different target address but also to
a different targetname.
This is needed to allow scenarious in active/active storage clusters where each
node had its own targetname, but maps the same volumes behind equal LUN ids.
For this non-RFC behaviour the environment variable LIBISCSI_ALLLOW_TARGETNAME_REDIRECT
has to be set.
Signed-off-by: Peter Lieven <pl@dlhnet.de>