Use appropriate python version

.travis.yml

@@ -1,29 +1,32 @@
 language: python
 sudo: required
 
-python:
-- "2.7"
-- "3.6"
-
 matrix:
   include:
     - dist: trusty
+      python: 2.7
+      env: dist="14.04 LTS trusty"
+    - dist: trusty
+      python: 3.6
       env: dist="14.04 LTS trusty"
 
 before_install:
 - sudo apt-get update -qq
 - sudo apt-get install -qq vlan
-- util/install.sh -n
+- PYTHON=`which python` util/install.sh -n
 
 install:
 - bash -c "if [ `lsb_release -rs` == '14.04' ]; then make codecheck; fi"
-- sudo util/install.sh -fnvw
+- pip install pexpect || pip3 install pexpect
+- util/install.sh -nfvw
 
 script:
-- echo "px import sys; print(sys.version_info)" | sudo mn -v output
+- alias sudo="sudo env PATH=$PATH"
-- sudo mn --test pingall
+- export PYTHON=`which python`
-- sudo python mininet/test/runner.py -v -quick
+- echo 'px import sys; print(sys.version_info)' | sudo $PYTHON bin/mn -v output
-- sudo python examples/test/runner.py -v -quick
+- sudo $PYTHON bin/mn --test pingall
+- sudo $PYTHON mininet/test/runner.py -v -quick
+- sudo $PYTHON examples/test/runner.py -v -quick
 
 notifications:
   email: