make sure the xunit output dir exists before trying to write to it
make sure the xunit output dir exists before trying to write to it

Fixes #1994

sul4bh/mocha,jjoos/mocha,Hacker0x01/mocha,boneskull/mocha,villesau/mocha,villesau/mocha,Shyp/mocha,aaroncrows/mocha,menelaos/mocha-solarized,JohnnyEstilles/mocha,JohnnyEstilles/mocha,hoverduck/mocha,sul4bh/mocha,menelaos/mocha-solarized,nightwatchjs/mocha-nightwatch,sul4bh/mocha,pumpupapp/mocha,outsideris/mocha,mochajs/mocha,Khan/mocha,apkiernan/mocha,santiagoaguiar/mocha,netei/mocha,menelaos/mocha-solarized,Hacker0x01/mocha,igwejk/mocha,boneskull/mocha,villesau/mocha,santiagoaguiar/mocha,igwejk/mocha,Shyp/mocha,apkiernan/mocha,adamgruber/mocha,hoverduck/mocha,ELLIOTTCABLE/mocha,pumpupapp/mocha,Khan/mocha,hoverduck/mocha,beatfactor/mocha,aaroncrows/mocha,jjoos/mocha,netei/mocha,ELLIOTTCABLE/mocha,jjoos/mocha,tswaters/mocha,adamgruber/mocha,santiagoaguiar/mocha,Hacker0x01/mocha,netei/mocha,ryanshawty/mocha,ryanshawty/mocha,JohnnyEstilles/mocha,beatfactor/mocha,beatfactor/mocha,nightwatchjs/mocha-nightwatch,rlugojr/mocha,ryanshawty/mocha,Shyp/mocha,ELLIOTTCABLE/mocha,adamgruber/mocha,mochajs/mocha,boneskull/mocha,tswaters/mocha,rlugojr/mocha,outsideris/mocha,Khan/mocha,nightwatchjs/mocha-nightwatch,apkiernan/mocha,rlugojr/mocha,aaroncrows/mocha,mochajs/mocha,hoverduck/mocha,pumpupapp/mocha,tswaters/mocha