Fix venv module installation on oraclelinux

Signed-off-by: Benoit Donneaux <benoit@leastauthority.com>

Author: btlogy

.circleci/Dockerfile.oraclelinux

@@ -1,22 +1,29 @@
 ARG TAG
 FROM oraclelinux:${TAG}
+# We need to declare TAG again to use it past FROM
+ARG TAG
 ARG PYTHON_VERSION
 
 ENV WHEELHOUSE_PATH /tmp/wheelhouse
 ENV VIRTUALENV_PATH /tmp/venv
 # This will get updated by the CircleCI checkout step.
 ENV BUILD_SRC_ROOT /tmp/project
 
+# Starting from v9, we need the EPEL repo for python3-virtualenv
+RUN dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-${TAG}.noarch.rpm
+
+# Use bash substitution to extract the major version of Python
+SHELL ["/bin/bash", "-c"]
 # XXX net-tools is actually a Tahoe-LAFS runtime dependency!
-RUN yum install --assumeyes \
+RUN dnf install --assumeyes \
     git \
     sudo \
     make automake gcc gcc-c++ \
     python${PYTHON_VERSION} \
     libffi-devel \
     openssl-devel \
     libyaml \
-    /usr/bin/virtualenv \
+    python${PYTHON_VERSION%%.*}-virtualenv \
     net-tools
 
 # Get the project source.  This is better than it seems.  CircleCI will