Fix downgrade in migration

In 63afba73813_ovs_tunnelendpoints_id_unique migration mistake in
usage drop_constraint parameter type_ and positional agruments name
and table_name.

Closes-Bug: #1243073

Change-Id: I60cd6e7f18b193b71f8f20759251b9f59a79965a
Apply six for metaclass

__metaclass__ cannot be used in python3.
six be used in general for python 3 compatibility.

Change-Id: Ib0d71b9676dc01390679396443575c05975d3b58
Closes-Bug: #1236648
Added check on plugin.supported_extension_aliases

Added check to neutron.api.extensions.PluginAwareExtensionManager
which raises an exception when an alias in the plugin's
`supported_extension_aliases` list is not found in the set of loaded
extension aliases. If an alias is missing, it means the extension for
that alias has not been loaded, has not been found, and the file is
missing from paths listed in `oslo.config.CONF.api_extensions_path`.

This guards against a common class of bugs in plugins,
such as typographical errors in the `supported_extension_aliases`
property.

Plugin changes:

* bigswitch.plugin: Moves api_extensions_path override to plugin's
__init__ method, similar to other plugins.

* cisco.n1kv.n1kv_neutron_plugin: Removes "policy_profile_binding" and
"network_profile_binding" as they don't exist in Neutron currently.
Removed override of api_extensions_path as it is loaded through
cisco.network_plugin.

* cisco.network_plugin: Renames "Cisco Credential" to "credential".
Adds api_extension_path override to plugin's __init__ method.

* metaplugin.meta_neutron_plugin: Avoids alias of empty string when
cfg.CONF.META.supported_extension_aliases is an empty string.

* midonet.plugin: Fixes regression of 98e16a06 from 715b16ac.

* nec.nec_plugin: Extended override of api_extensions_path to append
nec extensions path to existing configured path.

* nicira.NeutronPlugin: Extended override of api_extensions_path to
append NXP_EXT_PATH to existing configured path.

Fixes: bug 1225080

Change-Id: Idcaade221d83c611fcbd87b503b2c8377d106962
Rebind security groups only when they're updated

Update the security port bindings for a port only when they actually
differ from the stored value.

This will also avoid sending port_update notifications to the agent
even if nothing actually changes in the port configuration.

Closes-Bug: #1255183
Partial blueprint: neutron-tempest-parallel

Change-Id: I00c29dc97c46478433fdf08069a884bb78e5cd0a
Mocking ryu plugin notifier in ryu plugin test

Previously RPC notifier is not mocked in ryu plugin test and the
plugin tries to send RPC notifications. It may interact with
impl_fake RPC set up in previous tests by other plugin
and sometimes leads to unexpected ovs-vsctl invoking.

Change-Id: I11714a160faa4d3ded7f312c39afba0b426ccd8a
Closes-Bug: #1255421
Merge "Mocking ryu plugin notifier in ryu plugin test"
Merge "Fix downgrade in migration"
Merge "Rebind security groups only when they're updated"
Merge "Added check on plugin.supported_extension_aliases"
Merge "Apply six for metaclass"