Decoonfiguration of network fence

[#80656918]

Signed-off-by: Steve Powell <spowell@pivotal.io>
Persist and recover network fences

This is needed for pruning containers which were not in the snapshot
on garden restart. This often equates to all the containers when a
snapshot was not taken.

[#80656918]

Signed-off-by: Steve Powell <spowell@pivotal.io>