It turns out that the portmap plugin is not idempotent if its
executed in parallel.
The errors are caused due to a race of different instantiations
deleting the chains.
This patch does that the portmap plugin doesn't fail if the
errors are because the chain doesn't exist on teardown.
Signed-off-by: Antonio Ojea <antonio.ojea.garcia@gmail.com>
Namespace creation had an unergonomic interface and isn't used, except
for testing code. Remove it; downstream users should really be creating
their own namespaces
This change improves the performance of the portmap plugin and fixes
hairpin, when a container is mapped back to itself.
Performance is improved by using a multiport test to reduce rule
traversal, and by using a masquerade mark.
Hairpin is fixed by enabling masquerading for hairpin traffic.
