packaging: update Ubuntu docker build dependencies to Python 3
Changeset 7574ccd87200f02e updated the Debian docker builds to Python 3. In doing
so, the Ubuntu docker-based builds broke, as the Dockerfile does not
include the new dependencies as specified in `contrib/packaging/debian/control`.
This commit changes the dependencies in the Ubuntu Dockerfile template
to their Python 3 equivalents, fixing `make docker-ubuntu-bionic`.
Differential Revision: https://phab.mercurial-scm.org/D7810
[workspace]
members = ["hg-core", "hg-direct-ffi", "hg-cpython"]
exclude = ["chg", "hgcli"]