[CI] Prune networks older than 12h
[CI] Prune networks older than 12h

Previously we were using a filter which matched on the network name of
the networks we create. However, docker seems to have removed this
functionality, so now we just prune all unused networks which are more
than 12h old (no CI job should be taking more than 12h).


Reviewers: Enrico Olivelli <eolivelli@gmail.com>

This closes #2126 from ivankelly/ci-failure
sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,apache/bookkeeper,apache/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper