Unset DISPLAY to avoid importing ROOT when not showing plots (#314)

Author: jmcarcell

k4FWCore/scripts/k4run

@@ -262,9 +262,7 @@ def main():
     gaudi = gaudimain()
     if not opts.dry_run:
         if not opts.interactive_root:
-            from ROOT import gROOT
-
-            gROOT.SetBatch(True)
+            os.environ.pop("DISPLAY", None)
 
         # Do the real processing
         retcode = gaudi.run(opts.gdb)