Prevent symlinks to be added to the tree

Symlinks cannot be allowed because they are not supported by distutils.
Adding them results into package build failures.

This patch add a check that verifies that no symlinks can slip in.

Closes-bug: #1404605

Change-Id: I0d308127081bb2fa4ff7d7e0ed2f1b6e915163c9
PLUMgrid plugin: Fix for delete subnet with admin context

When delete call using admin for a subnet created from a
non-admin project is made, the tenant_id passed to backend
happened to be of admin project. This commit fixes the issues
by getting the correct tenant_id.

Closes-Bug: 1404688
Change-Id: Id21c38610ed73defb937d971a7aade57713541c0
ipv6: set OtherConfig flag for DHCPv6 stateless subnets

In case of DHCPv6 stateless subnets, we should inform DHCP clients about
other configuration values available from DHCP server. This is done by
setting O (other) flag in RAs, which is controlled by AdvOtherConfigFlag
setting in radvd case.

Since radvd configuration file becomes quite complex, migrated its
generation to Jinja2.

Added a basic unit test that checks that flag is set for stateless mode
and not SLAAC. For stateful, it doesn't really matter whether other flag
is set, so no need to expect any value of it.

No more unit tests seem to be needed: conditional prefix generation is
already covered in test_l3_agent, and other statements are common for
all ipv6_ra_modes.

Change-Id: I1ddad3e1f5efce2b6da4ec00b9294e08fe1e85dd
Closes-Bug: #1397022
Merge "ipv6: set OtherConfig flag for DHCPv6 stateless subnets"
Merge "PLUMgrid plugin: Fix for delete subnet with admin context"
Merge "Prevent symlinks to be added to the tree"