* update heronpy release scripts for python3
 * update dist Dockerfiles to only use python3
 * remove python2 from docker images
 * upgrade pylint for python3 support
 * upgrade PEX so transative dependencies are captured

Additionally:
 * fix Ubuntu 16.04 images
 * fix linting issues found by newer pylint

There is an issue with encapsulation in the builds where the global python3 environment is used
while PEX installs a nested transitive dependency of pylint: `pylint>astroid>wrapt`. This seems
to be because of logic in its setup.py which can be disabled with `WRAPT_INSTALL_EXTENSIONS=false`

The issue encountered was protocolbuffers/protobuf#1491 which
may be fixed by a pending PR to protoc, or with a switch to the official protobuf rules
and the import_prefix parameter to proto_library.

 * bytes vs str issues
 * update kazoo
 * order of processes in executor test changed due to dict ordering?
 * some places needed / switched to // - may be more not caught by tests
 * add travis_wait as some stages going over 10 minutes without output in CI

TODO:
 * make sure the kazoo upgrade is correct, it was done only by updating package versoin

 * use universal_newline in popen instead of text in Popen for py3.6
 * fix bytes/str issues in deserialisation
 * fix file open modes
 * use set instead of sets.Set
 * fix __import__(level) default

 * use new external pkg_* rules
 * add python to compile docker images until pkg_*
 * add --host_force_python=PY3 to other bazel.rc files

 * use kind to create ephemeral clusters
 * start consolidating scripts with python