isis: T8094: bugfix config migration from 1.3.0-rc1 -> 1.4

While producing all configtest assert files for VyOS 1.4 it was noted that
the the isis-small testcase from fails. This config fragment is not properly
migrated when updating from VyOS 1.3.0-rc1 -> 1.4 and using IS-IS.

protocols {
    isis FOO {
        interface eth1 {
           bfd
        }
        net 49.0001.1921.6800.1002.00
        redistribute {
            ipv4 {
                connected {
                    level-2 {
                        route-map EXPORT-ISIS
                    }
                }
            }
        }
    }
}

and results in loosing IS-IS connectivity. This is due the fact that
config.rename() does not work when only using the base tagNode.

1 files changed, 14 insertions, 6 deletions

diff --git a/src/migration-scripts/isis/0-to-1 b/src/migration-scripts/isis/0-to-1
index 052dbc8a8..3a9735d29 100644
--- a/src/migration-scripts/isis/0-to-1
+++ b/src/migration-scripts/isis/0-to-1
@@ -24,13 +24,21 @@ def migrate(config: ConfigTree) -> None:
         # Nothing to do
         return
 
-    # We need a temporary copy of the config
-    tmp_base = ['protocols', 'isis2']
-    config.copy(base, tmp_base)
+    if not config.is_tag(base):
+        # Nothing to do
+        exit(0)
+
+    # Get IS-IS domain ID
+    domain_id = config.list_nodes(base)
+    if domain_id:
+        # We need a temporary copy of the config
+        tmp_base = ['protocols', 'isis2']
+        config.copy(base + domain_id, tmp_base)
 
     # Now it's save to delete the old configuration
     config.delete(base)
 
-    # Rename temporary copy to new final config (IS-IS domain key is static and no
-    # longer required to be set via CLI)
-    config.rename(tmp_base, 'isis')
+    # Rename temporary node to new final config (IS-IS domain key is static and
+    # no longer required to be set via CLI)
+    if config.exists(tmp_base):
+        config.rename(tmp_base, 'isis')