Add python in travis ci for paddle version command

.travis.yml

@@ -25,7 +25,9 @@ addons:
       - git
       - build-essential
       - libatlas-base-dev
+      - python
       - python-pip
+      - python2.7-dev
       - curl
       - graphviz
       - clang-format-3.8

paddle/api/test/CMakeLists.txt

 add_test(NAME test_swig_api
-    COMMAND bash ${PROJ_ROOT}/paddle/api/test/run_tests.sh ${PYTHON_EXECUTABLE} ${PYTHON_INSTALL_DIR}/bin/pip)
+    COMMAND bash ${PROJ_ROOT}/paddle/api/test/run_tests.sh ${PYTHON_EXECUTABLE})

paddle/api/test/run_tests.sh

@@ -20,10 +20,6 @@ popd > /dev/null
 
 cd $SCRIPTPATH
 
-# rm -rf .test_env
-# virtualenv .test_env
-# source .test_env/bin/activate
-
 $1 -m pip install ../../dist/*.whl
 
 test_list="testArguments.py testGradientMachine.py testMatrix.py  testVector.py testTrain.py testTrainer.py"