ansible: use Python 3.8 in CentOS 7 container

Current versions of tap2junit require Python > 3.7. The default
python3 package on CentOS 7 is Python 3.6.

ansible/roles/docker/templates/centos7.Dockerfile.j2

@@ -14,6 +14,7 @@ ENV DESTCPU {{ arch }}
 ENV ARCH {{ arch }}
 
 RUN yum -y update && \
+    yum install -y centos-release-scl && \
     yum install -y \
       gcc \
       gcc-c++ \
@@ -22,12 +23,12 @@ RUN yum -y update && \
       java-11-openjdk-headless \
       pkgconfig \
       curl \
-      python3-pip \
+      rh-python38-python-pip \
       fontconfig-devel \
       libtool \
       automake
 
-RUN pip3 install tap2junit=={{ tap2junit_version }}
+RUN . /opt/rh/rh-python38/enable && pip3 install tap2junit=={{ tap2junit_version }}
 
 RUN groupadd --gid {{ server_user_gid.stdout_lines[0] }} {{ server_user }}
 
@@ -39,7 +40,6 @@ RUN yum -y install ccache
 RUN yum -y install glibc-devel zip unzip perl openssh-clients libgomp make scl-utils avahi kernel-devel policycoreutils-python which libgfortran
 RUN rpm -ivh https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-runtime-6.1-1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-elfutils-libs-0.168-3.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-systemtap-runtime-3.0-8s.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-ltrace-0.7.91-17.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-strace-4.12-3.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-systemtap-client-3.0-8s.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-gcc-gfortran-6.3.1-3.1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-binutils-2.27-12.el7.1.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-elfutils-libelf-0.168-3.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-elfutils-0.168-3.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-gdb-7.12.1-48.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-make-4.1-3.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-gcc-c++-6.3.1-3.1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-memstomp-0.1.5-5.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-dwz-0.12-1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-systemtap-3.0-8s.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-toolchain-6.1-1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-gcc-6.3.1-3.1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-valgrind-3.12.0-1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-libstdc++-devel-6.3.1-3.1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-oprofile-1.1.0-4.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-systemtap-devel-3.0-8s.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-perftools-6.1-1.el7.aarch64.rpm https://buildlogs.centos.org/c7-devtoolset-6.aarch64/Packages/devtoolset-6-6.1-1.el7.aarch64.rpm
 
-RUN yum -y install centos-release-scl
 RUN yum -y install devtoolset-8 devtoolset-8-libatomic-devel
 
 VOLUME /home/{{ server_user }}/ /home/{{ server_user }}/.ccache
@@ -49,6 +49,7 @@ USER iojs:iojs
 ENV CCACHE_TEMPDIR /home/iojs/.ccache/{{ item.name }}
 
 CMD cd /home/iojs \
+  && . /opt/rh/rh-python38/enable \
   && curl https://ci.nodejs.org/jnlpJars/agent.jar -O \
   && java -Xmx{{ server_ram|default('128m') }} \
           -jar /home/{{ server_user }}/agent.jar \