CI: Update python dependency on Ubuntu rolling

Package 'python' no longer exists. Replace it with 'python3'
Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Reza Arbab <arbab@linux.ibm.com>

opal-ci/Dockerfile-ubuntu-rolling

@@ -2,7 +2,7 @@ FROM ubuntu:rolling
 ENV DEBIAN_FRONTEND    noninteractive
 RUN apt-get update -qq
 RUN if [ `arch` != "ppc64le" ]; then apt-get install -y gcc-powerpc64le-linux-gnu; fi
-RUN apt-get install -y gcc ccache expect libssl-dev wget curl xterm device-tree-compiler build-essential gcc python g++ pkg-config libz-dev libglib2.0-dev libpixman-1-dev libfdt-dev git libstdc++6 valgrind libtcl8.6 qemu-system-ppc libmbedtls-dev
+RUN apt-get install -y gcc ccache expect libssl-dev wget curl xterm device-tree-compiler build-essential gcc python3 g++ pkg-config libz-dev libglib2.0-dev libpixman-1-dev libfdt-dev git libstdc++6 valgrind libtcl8.6 qemu-system-ppc libmbedtls-dev
 RUN apt-get install -y gcc-arm-linux-gnueabi || true
 RUN if [ `arch` = "x86_64" ]; then curl -O http://public.dhe.ibm.com/software/server/powerfuncsim/p9/packages/v1.1-0/systemsim-p9-1.1-0-trusty_amd64.deb; dpkg -i systemsim-p9-1.1-0-trusty_amd64.deb; fi
 RUN if [ `arch` = "x86_64" ]; then curl -O http://public.dhe.ibm.com/software/server/powerfuncsim/p10/packages/v1.2-1/ubuntu2004/systemsim-p10_1.2-1_amd64.deb; dpkg -i systemsim-p10_1.2-1_amd64.deb; fi