Fix some new pylint "W" warnings

After updating pylint, it started emitting additional "W"
warnings in some cases, fix some of them.

  modified-iterating-list,
  implicit-str-concat,
  global-variable-not-assigned

Trivialfix

Change-Id: I7deb5f1e0aa2852cb033c78dcb4c8bc87e34be1e

.pylintrc

@@ -59,13 +59,10 @@ disable=
  raise-missing-from,
  arguments-renamed,
  broad-exception-raised,
- modified-iterating-list,
  unspecified-encoding,
  missing-timeout,
- implicit-str-concat,
  redundant-u-string-prefix,
  unused-private-member,
- global-variable-not-assigned,
 # "C" Coding convention violations
  consider-iterating-dictionary,
  consider-using-enumerate,

neutron/agent/linux/iptables_firewall.py

@@ -731,7 +731,7 @@ class IptablesFirewallDriver(firewall.FirewallDriver):
 
     def _drop_invalid_packets(self, iptables_rules):
         # Always drop invalid packets
-        iptables_rules += [comment_rule('-m state --state ' 'INVALID -j DROP',
+        iptables_rules += [comment_rule('-m state --state INVALID -j DROP',
                                         comment=ic.INVALID_DROP)]
         return iptables_rules
 

neutron/common/utils.py

@@ -769,7 +769,7 @@ def attach_exc_details(e, msg, args=_NO_ARGS_MARKER):
 def extract_exc_details(e):
     for attr in ('_error_context_msg', '_error_context_args'):
         if not hasattr(e, attr):
-            return u'No details.'
+            return 'No details.'
     details = e._error_context_msg
     args = e._error_context_args
     if args is _NO_ARGS_MARKER:

neutron/plugins/ml2/drivers/ovn/mech_driver/ovsdb/ovn_db_sync.py

@@ -284,7 +284,7 @@ class OvnNbSynchronizer(OvnDbSynchronizer):
 
         # Remove the common ones
         for na in list(neutron_acls):
-            for ovn_a in ovn_acls:
+            for ovn_a in ovn_acls.copy():
                 if all(item in na.items() for item in ovn_a.items()):
                     neutron_acls.remove(na)
                     ovn_acls.remove(ovn_a)

neutron/services/trunk/drivers/openvswitch/agent/driver.py

@@ -104,8 +104,5 @@ def init_handler(resource, event, trigger, payload=None):
 
 def unregister():
     """Cleanup fanout queues"""
-    global TRUNK_SKELETON
-    try:
+    if TRUNK_SKELETON:
         TRUNK_SKELETON.unregister()
-    except AttributeError:
-        pass