Workaround a bug in pip which fails to install pylint in Ubuntu Trusty

We use a virtualenv where pip works fine.

Author: barisione

.travis.yml

@@ -29,10 +29,14 @@ before_install:
             coreutils \
             python2.7 \
             python3-pip \
-            python3.4 \
+            python3.5 \
             shellcheck \
             && \
-        sudo pip3 install pylint; \
+        sudo pip3 install virtualenv && \
+        virtualenv --python=python3.5 venv-for-travis && \
+        . ./venv-for-travis/bin/activate && \
+        pip install pylint && \
+        deactivate; \
     fi
 
 script:

run-checks

@@ -8,7 +8,20 @@ echo "== RUNNING TESTS =="
 echo
 
 echo "== RUNNING PYLINT =="
+readonly venv_activate=./venv-for-travis/bin/activate
+if [ -e "$venv_activate" ]; then
+    echo "Using virtualenv: $venv_activate"
+    # shellcheck disable=SC1090
+    . "$venv_activate"
+else
+    echo "No virtualenv"
+fi
+
 ./tests/run-pylint
+
+if [ -e "$venv_activate" ]; then
+    deactivate
+fi
 echo
 
 echo "== RUNNING SHELLCHECK =="