Upgrade pip in virtualenv
This fixes the build on trusty.
@@ -618,6 +618,7 @@ installapiserver()
unset_opt=$(shopt -po nounset)
set +u
(source /opt/appscale_api_server/bin/activate && \
+ pip install -U pip && \
pip install ${APPSCALE_HOME}/AppControllerClient ${APPSCALE_HOME}/common \
${APPSCALE_HOME}/APIServer)
eval ${unset_opt}
