Fix ovs-vsctl call in add_tunnel_port()

When a new GRE tunnel is created OVS agent calls ovs-vsctl
incorrectly. Command:

    sudo ovs-vsctl --timeout=2 --may-exist add-port br-tun gre-1

is produced instead of correct one:

   sudo ovs-vsctl --timeout=2 -- --may-exist add-port br-tun gre-1

Fixes bug 1227675

Change-Id: I010961658a37028e41621c4a529b5a14e7587c7f
Cisco plugin portbinding extension support

This commit adds portbinding extension support to the Cisco plugin.

Change-Id: I87554607860b040b693edeecc2706ca8edbe49b6
Fixes: Bug #1218033
Change header from LLC to Foundation

Change-Id: I11d7e734ae56568f2387a208efe0d1487377cbf9
Closes-Bug: #1214176
Merge "Cisco plugin portbinding extension support"
Merge "Change header from LLC to Foundation"
Merge "Fix ovs-vsctl call in add_tunnel_port()"
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_extension_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.
Extended override of api_extensions_path to append cisco extensions
path to existing configured path.

* 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 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