ci,build: add Ubuntu 20.04 docker builds

Ubuntu 20.04 should be out in a couple of weeks. But docker images are
currently available.
Start using them.
They get pulled from here:
   https://hub.docker.com/_/ubuntu

Also, Ubuntu 20.04 seems to start phasing out some Python2 stuff, so we
need to install python3-pip vs python-pip, which should work on older
distros as well.

Signed-off-by: Alexandru Ardelean <[email protected]>

.travis.yml

@@ -69,6 +69,11 @@ matrix:
       dist: bionic
       env:
         - EXTRA_SSH=-oHostKeyAlgorithms=+ssh-dss
+    - os: linux
+      env:
+        - OS_TYPE=ubuntu_docker
+        - OS_VERSION=focal
+        - EXTRA_SSH=-oHostKeyAlgorithms=+ssh-dss
     - compiler: "gcc"
       os: osx
       osx_image: xcode10.1

CI/travis/before_install_linux

@@ -22,7 +22,8 @@ handle_default() {
 	sudo DEBIAN_FRONTEND=noninteractive apt-get install -y cmake graphviz \
 		libaio-dev libavahi-client-dev \
 		libavahi-common-dev libusb-1.0-0-dev libxml2-dev rpm tar \
-		bzip2 gzip flex bison git python-pip
+		bzip2 gzip flex bison git lsb-release python3-pip
+
 	if [ -n "${GH_DOC_TOKEN}" ] ; then
 		sudo apt-get install -y doxygen
 	fi