Merge branch 'maint-0.2.9' into maint-0.3.5

changes/ticket31919_bionic

+  o Minor features (continuous integration):
+    - Use Ubuntu Bionic images for our Travis CI builds, so we can get
+      a recent version of coccinelle. But leave chutney on Ubuntu Trusty,
+      until we can fix some Bionic permissions issues (see ticket 32240).
+      Related to ticket 31919.