virsh: tweak previous domblkstat patch

virsh: tweak previous domblkstat patch

Translators are likely to botch trailing spacing; by doing the
formatting outside of the translation, we can generally get
better alignment.  Also, for consistency, use 'bytes read' to
match 'bytes written'.

* tools/virsh.c (domblkstat_output): Drop trailing space. Tweak
rd_bytes output.
(cmdDomblkstat, DOMBLKSTAT_LEGACY_PRINT): Update formatting.