iscsi: Add timeout option

iscsi: Add timeout option

This was previously only available with -iscsi. Again, after this patch,
the -iscsi option only takes effect if an URL is given. New users are
supposed to use the new driver-specific option.

All -iscsi options have a corresponding driver-specific option for the
iscsi block driver now.

Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>