python: adding a back python27Full

to make pypi2nix work with old and new nixpkgs. in future nixos release
we can remove it, but at least one release cycle of deprecation would
be nice.

pkgs/top-level/all-packages.nix

@@ -5507,6 +5507,7 @@ in
   pythonFull = python.override{x11Support=true;};
   python2Full = python2.override{x11Support=true;};
   python3Full = python3.override{x11Support=true;};
+  python27Full = python2Full;
 
   # pythonPackages further below, but assigned here because they need to be in sync
   pythonPackages = python2Packages;