fix: what bandit and the remaining lint rules found

- Long lines are wrapped: the get_environment awk command is split into
  adjacent string literals, the rollback message and the system mixin's
  docstring are wrapped; the command and the text are unchanged.
- The two except Exception: pass (the snmpd community in get_snmp_config,
  the network VLANs in get_ssids) now log at debug level (B110), so a
  swallowed failure leaves a trace.
- tests: raise ... from exc, unused loop variable.

napalm_openwrt/config_mixin.py

@@ -91,7 +91,8 @@ class OpenWrtConfigMixin(ConfigLifecycleMixin):
         """
         if self._backup_config is None:
             raise CommandErrorException(
-                "No backup configuration available – commit_config has not been called in this session."
+                "No backup configuration available – "
+                "commit_config has not been called in this session."
             )
 
         escaped = self._backup_config.replace("'", "'\\''")