Rewrite zebra policy to XML/Python format
```
vyos@r2-roll# set policy
+> access-list
+> access-list6
+> as-path-list
+> community-list
+> extcommunity-list
+> ipv6-route
+> large-community-list
+> prefix-list
+> prefix-list6
+> route-map
```
Adding 1000 prefix-lists in the VyOS CLI takes **~3m26s78**
Adding 1000 prefix-lists in FRR itself takes **~0m0.424s**
Old backend bash checks very slow.
An example https://github.com/vyos/vyatta-cfg-quagga/blob/current/templates/policy/prefix-list/node.tag/rule/node.def