* tools/virsh.c: format strings display for virsh nodecpustats --percent.

* how to reproduce?

% virsh nodecpustats --percent
usage:            2.0%
    user  :       1.0%
    system:       1.0%
idle  :          98.0%
iowait:           0.0%

* after format strings

% virsh nodecpustats --percent
usage:            2.0%
user:             1.0%
system:           1.0%
idle:            98.0%
iowait:           0.0%
Signed-off-by: NAlex Jia <ajia@redhat.com>