Add cobertura XML coverage report
Add cobertura XML coverage report

When running an HTML report, also output a cobertura XML file that our
buildbot can read.

Change-Id: I24351a7d9d693e6286332c5cb4ed694c0347c31d

shaka-project/shaka-player,vimond/shaka-player,Ross-cz/shaka-player,russitto/shaka-player,indiereign/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,brightcove/shaka-player,Ross-cz/shaka-player,brightcove/shaka-player,indiereign/shaka-player,TheModMaker/shaka-player,vimond/shaka-player,tvoli/shaka-player,brightcove/shaka-player,shaka-project/shaka-player,russitto/shaka-player,shaka-project/shaka-player,Ross-cz/shaka-player,TheModMaker/shaka-player,TobbeEdgeware/shaka-player,vimond/shaka-player,indiereign/shaka-player,tvoli/shaka-player,russitto/shaka-player,TobbeEdgeware/shaka-player,TobbeEdgeware/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,shaka-project/shaka-player