storage: fs: Don't attempt directory creation if it already exists
storage: fs: Don't attempt directory creation if it already exists

The current code attempts to handle this, but it only catches mkdir
failing with EEXIST. However if say trying to build /tmp for an
unprivileged qemu:///session, mkdir will fail with EPERM.

Rather than catch any errors, just don't attempt mkdir if the directory
already exists.

libvirt/libvirt,eskultety/libvirt,taget/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,crobinso/libvirt,olafhering/libvirt,jfehlig/libvirt,nertpinx/libvirt,datto/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,jfehlig/libvirt,jardasgit/libvirt,jfehlig/libvirt,datto/libvirt,VenkatDatta/libvirt,crobinso/libvirt,eskultety/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,libvirt/libvirt,crobinso/libvirt,andreabolognani/libvirt,zippy2/libvirt,olafhering/libvirt,agx/libvirt,nertpinx/libvirt,jardasgit/libvirt,jardasgit/libvirt,libvirt/libvirt,taget/libvirt,datto/libvirt,datto/libvirt,agx/libvirt,andreabolognani/libvirt,taget/libvirt,nertpinx/libvirt,rlaager/libvirt,eskultety/libvirt,datto/libvirt,agx/libvirt,agx/libvirt,zippy2/libvirt,agx/libvirt,jardasgit/libvirt,libvirt/libvirt,rlaager/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,rlaager/libvirt,taget/libvirt,jfehlig/libvirt,olafhering/libvirt,olafhering/libvirt,crobinso/libvirt,jardasgit/libvirt,nertpinx/libvirt,rlaager/libvirt,zippy2/libvirt,eskultety/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,zippy2/libvirt,nertpinx/libvirt,taget/libvirt,rlaager/libvirt,fabianfreyer/libvirt,eskultety/libvirt