Fix neutron-lbaas-agent issue

Currently, you cannot converge a CentOS (and presumably SUSE) node when
balancer recipe is in run list.  This is because no neutron_lb_packages
attributes have been specified.

Change-Id: I4d3428c69c7e6098b13aa15bf07e61defdc2a207
Closes-Bug: #1283237
Point to correct lbaas_agent.ini file

On CentOS / Ubuntu, lbaas agent fails to start as we drop in a config
in a non-standard location.  The stock distro-provided config is also
problematic as it doesn't have a default interface_driver set which
prevents the service from starting.

This change defaults all distros to use /etc/neutron/lbaas_agent.ini
and tidies up ownership/mode of the dropped file.

Change-Id: I919e535989c5ec05ee196235fbd528eb971cbb05
Closes-Bug: #1283237
Merge "Point to correct lbaas_agent.ini file"
Merge "Fix neutron-lbaas-agent issue"