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: Ie8c1710488974bc193c930f5df10909114371eb3

t/Dockerfile

@@ -12,6 +12,11 @@ RUN apt-get install --assume-yes git abi-compliance-checker
 
 RUN echo './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
+
 WORKDIR /code/
 
 ################################################################################