fix(iscsi): do not exit in handle_netroot() if discovery failed

User may specify multiple netroot in cmdline, failed to connect one netroot
do not mean all netroot are not accessible. So if one netroot failed, do
not exit the discovery and login flow.

Signed-off-by: Wenchao Hao <haowenchao@huawei.com>

modules.d/95iscsi/iscsiroot.sh

@@ -229,7 +229,7 @@ handle_netroot() {
             echo "$target"
         done
     })
-    [ -z "$targets" ] && echo "Target discovery to $iscsi_target_ip:${iscsi_target_port:+$iscsi_target_port} failed with status $?" && exit 1
+    [ -z "$targets" ] && warn "Target discovery to $iscsi_target_ip:${iscsi_target_port:+$iscsi_target_port} failed with status $?" && return 1
 
     found=
     for target in $targets; do