Provide default api_extensions_path for NEC plugin

[Akihiro Motoki]

NEC plugin has a plugin specific extension in its plugin directory.
api_extension_path must be set in quantum.conf to enable quantum-server to load the extension,
but users sometimes forget to set it.

It provides better usability if api_extensions_path is set appropriately by default

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/22949

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/22949
Committed: http://github.com/openstack/quantum/commit/c85c9c43336313711b78efdcd0123b20cd3c5899
Submitter: Jenkins
Branch: master

commit c85c9c43336313711b78efdcd0123b20cd3c5899
Author: Akihiro MOTOKI <email address hidden>
Date: Tue Feb 26 12:37:37 2013 +0900

    Set default api_extensions_path for NEC plugin

    NEC plugin has a plugin specific extension in its plugin directory.
    api_extension_path must be set in quantum.conf to enable quantum-server
    to load the extension, but users sometimes forget to set it. It provides
    better usability if api_extensions_path is set appropriately by default.

    Fixes bug 1133099

    Change-Id: Ifa6d8a4f6bd30be5c6641c127ffcfaab5ff20b47