Dockerfiles could use a "tidy"

It was noticed that some of the Dockerfiles result in more layers than necessary and the source is occasionally removed in a different layer than where it is installed.

An example is Dockerfile.openmpi

# UCX. There is stuff to build Debian packages, but it seems not too polished.
ENV UCX_VERSION 1.6.1
RUN git clone --branch v${UCX_VERSION} --depth 1 \
              https://github.com/openucx/ucx.git
RUN    cd ucx \
    && ./autogen.sh \
    && ./contrib/configure-release-mt --prefix=/usr/local \
    && make -j$(getconf _NPROCESSORS_ONLN) install
RUN rm -Rf ucx*

This likely should just be and ENV and then a single RUN.