weave: Upgrade to 2.4.0

Upstream Changes:

-   weave 2.4.0 (https://github.com/weaveworks/weave/releases/tag/v2.4.0)
-   Support `externalTrafficPolicy: Local` (https://github.com/weaveworks/weave/issues/2924)
-   Make the ipset list size bigger (https://github.com/weaveworks/weave/pull/3305)
-   Break out of kube rm-peers loop if nothing changes (https://github.com/weaveworks/weave/pull/3317)

Our Changes:

-   Revamp weave-net.yml.j2 with upstream changes
-   Add more variables for customization
-   Replace WEAVE_PASSWORD with k8s secret
-   Remove hard-corded seed mode support, in favor of variables customization