CDRIVER-4156 use Python from toolchain on Ubuntu 14.04 Evergreen hosts

Author: rcsanchez97

.evergreen/integration-tests.sh

@@ -117,6 +117,9 @@ case "$OS" in
       if [ -f /opt/python/2.7/bin/python ]; then
          # Python toolchain installation.
          PYTHON=/opt/python/2.7/bin/python
+      elif [ "x$(lsb_release -cs)" = "xtrusty" -a -f /opt/mongodbtoolchain/v2/bin/python ]; then
+         # Python toolchain installation.
+         PYTHON=/opt/mongodbtoolchain/v2/bin/python
       else
          PYTHON=python
       fi