iohelper: use saferead if later write with O_DIRECT
iohelper: use saferead if later write with O_DIRECT

One of the usecases of iohelper is to read from pipe and write
to file with O_DIRECT. As we read from pipe we can have partial
read and then we fail to write this data because output file
is open with O_DIRECT and buffer size is not aligned.

Signed-off-by: Jiri Denemark <62bdf77dc47919a4d59a91822129d14633cfca81@redhat.com>

crobinso/libvirt,nertpinx/libvirt,jardasgit/libvirt,nertpinx/libvirt,zippy2/libvirt,andreabolognani/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,zippy2/libvirt,nertpinx/libvirt,zippy2/libvirt,andreabolognani/libvirt,crobinso/libvirt,olafhering/libvirt,fabianfreyer/libvirt,crobinso/libvirt,jardasgit/libvirt,eskultety/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,jardasgit/libvirt,eskultety/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,olafhering/libvirt,eskultety/libvirt,fabianfreyer/libvirt,eskultety/libvirt,eskultety/libvirt,andreabolognani/libvirt,zippy2/libvirt,olafhering/libvirt,jardasgit/libvirt,andreabolognani/libvirt,libvirt/libvirt,libvirt/libvirt,jfehlig/libvirt,libvirt/libvirt,jfehlig/libvirt,jfehlig/libvirt,crobinso/libvirt,olafhering/libvirt,libvirt/libvirt,jardasgit/libvirt