More accumulated dataproc Dockerfile changes (and miscellanea)

[jmarshall]

Further fixes that had to be applied to get a successful dataproc image build:

• It also needed venv.
• It turns out the Jammy python3-build package is old and broken (cf https://github.com/pypa/build/issues/215#issuecomment-1335839224) so we install the current version via pip instead.
• Docker I think defaults to using dash, so avoid a bashism to prevent the default STRIP_PIP_VERSIONS=false producing a (harmless) error message.

Also some unrelated string formatting miscellanea that I've had lying around in my checkout for a while.