starpu_fxt_tool: add call to starpu_drivers_preinit

So the drivers names are loaded and fix workers named unknow
2 jobs for !14 with fix_fxt_tool in 13 minutes and 6 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Build
passed #978632
build

00:05:40

 
  Deploy
passed #978633
deploy

00:07:25