TT#8635 set umask for files created by docker

tests made in 'docker run' create files with 'root' owner and ws-cleanup
plugin can't delete them after. Fixing umask here to allow files
deletion.

Change-Id: I501181f3fe074e57a777ab6a0eac4edfddd70566

t/Dockerfile

@@ -33,6 +33,11 @@ RUN ln -s /usr/bin/xvfb-chromium /usr/bin/chromium-browser
 
 RUN echo "cd /code && ./t/testrunner" >/root/.bash_history
 
+# Create files with mode 666 and folders with mode 777 which
+# allows to delete the temporary files (aka results) for
+# non-root users (like 'jenkins' or 'developer's laptop local user')
+RUN echo 'umask 0' >>/root/.bashrc
+
 RUN ln -s /home/selenium/chromedriver /usr/bin/chromedriver
 
 COPY jenkins_docker_run /home/selenium/