tools/kvm_stat: suppress usage information on command line errors
Errors while parsing the '-g' command line argument result in display of
usage information prior to the error message. This is a bit confusing,
as the command line is syntactically correct.
To reproduce, run 'kvm_stat -g' and specify a non-existing or inactive
guest.
Signed-off-by: Stefan Raspl <raspl@linux.vnet.ibm.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>