Delete duplicate section in nova.conf.

It has no effect - typo when we put the config file together.

Change-Id: I0be758cd1192c55432e26199dcadedcad9823d84
Allow enabling Neutron orchestrated PXE.

This is off by default for compatibility with older Neutron's, but we
need it to get rid of file injection. As we want to support Havana
too, we probably need to be able to run both with and without this, so
making it an option seems reasonable.

Change-Id: If29d1e38930975b763bb9d10b37fb3ae040da96d