travis: improve python version test coverage

Currently travis declares ancient python 2.4 is desired. Update that to
2.6 which is the oldest version any targetted distros still needs. If we
just list a python 3 version at the top level this will double the
number of travis jobs we run which is unreasonable.

So arbitrarily pick the clang test matrix entries to build with python
3.0 and 3.6, to extend coverage of python versions, without increasing
job count or build time.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <20180116134217.8725-14-berrange@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

.travis.yml

@@ -1,7 +1,7 @@
 sudo: false
 language: c
 python:
-  - "2.4"
+  - "2.6"
 compiler:
   - gcc
 cache: ccache
@@ -115,15 +115,17 @@ matrix:
         - sudo apt-get build-dep -qq qemu
         - wget -O - http://people.linaro.org/~alex.bennee/qemu-submodule-git-seed.tar.xz | tar -xvJ
         - git submodule update --init --recursive
-    # Trusty System build with latest stable clang
+    # Trusty System build with latest stable clang & python 3.0
     - sudo: required
       addons:
       dist: trusty
       language: generic
       compiler: none
+      python:
+        - "3.0"
       env:
         - COMPILER_NAME=clang CXX=clang++-3.9 CC=clang-3.9
-        - CONFIG="--disable-linux-user --cc=clang-3.9 --cxx=clang++-3.9"
+        - CONFIG="--disable-linux-user --cc=clang-3.9 --cxx=clang++-3.9 --python=/usr/bin/python3"
       before_install:
         - wget -nv -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add -
         - sudo apt-add-repository -y 'deb http://llvm.org/apt/trusty llvm-toolchain-trusty-3.9 main'
@@ -134,15 +136,17 @@ matrix:
         - git submodule update --init --recursive
       before_script:
         - ./configure ${CONFIG} || cat config.log
-    # Trusty Linux User build with latest stable clang
+    # Trusty Linux User build with latest stable clang & python 3.6
     - sudo: required
       addons:
       dist: trusty
       language: generic
       compiler: none
+      python:
+        - "3.6"
       env:
         - COMPILER_NAME=clang CXX=clang++-3.9 CC=clang-3.9
-        - CONFIG="--disable-system --cc=clang-3.9 --cxx=clang++-3.9"
+        - CONFIG="--disable-system --cc=clang-3.9 --cxx=clang++-3.9 --python=/usr/bin/python3"
       before_install:
         - wget -nv -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add -
         - sudo apt-add-repository -y 'deb http://llvm.org/apt/trusty llvm-toolchain-trusty-3.9 main'