Devstack support for Neutron VPNaaS

Includes two enhancements to support VPNaaS and allow other
vendor implementation support. Goal is to provide a solution
for VPN .ini files until a more general solution can be defined
to handle all reference and vendor .ini files.

First, the /opt/stack/neutron/etc/vpn_agent.ini file is copied
to /etc/neutron, to allow the selected device drivers for agent
to be specified. Both reference and vendor implementations can
be uncommented in this file, prior to stacking.

Second, to allow vendor VPN implementations to provide an .ini
file to the agent at start-up time, an environment variable is
defined and can be set in the localrc to specify one or more
.ini files. The desire is NOT to include vendor settings in the
global vpn_agent.ini.

Change-Id: I5370ee57bbe326eff505a53055da4fddc0838de4
Closes-Bug: 1301552
Set parameters for OpenDaylight ML2 driver

Now that https://review.openstack.org/#/c/85589/ is merged, the
OpenDaylight ML2 driver requires that url, username and password
parameters are set.

Change-Id: Iecbdd3275387bea145a5d274d359a15eceaee6b7
Closes-Bug: #1304226
Enabled non-root users to read nfs_shares.conf.

If you use the cinder NFS driver, it will create a file called
nfs_shares.conf, containing a list of NFS shares cinder can
use.  The file is created with 660 permissions and owned by
root:root.  When c-vol starts, it has problems reading
nfs_shares.conf, resulting in a "[Errno 13] Permission denied:
'/etc/cinder/nfs_shares.conf'".  This patch creates
nfs_shares.conf without using sudo, so c-vol can at least
read it.

Change-Id: Ifce2bd4b9ff2191445a1964c1ce09c823d096d68
Closes-Bug: #1297916
Merge "Devstack support for Neutron VPNaaS"
Merge "Enabled non-root users to read nfs_shares.conf."
Merge "Set parameters for OpenDaylight ML2 driver"