virsh.sysinfo: Don't fail over a single space

Found an instance on a test machine where the processor string was
prefixed with a space from dmidecode:

        Version: P73
        Version: Not Specified
        Version: Not Specified
        Version:  Intel(R) Xeon(R) CPU E5-2470 0 @ 2.30GHz
        Version:  Intel(R) Xeon(R) CPU E5-2470 0 @ 2.30GHz
        Specification Version: 2.0

which caused a failure because libvirt will strip leading spaces. So
just strip the dmicode output as well to avoid the issue