tools/kvm_stat: sort '-f help' output

Sort the fields returned by specifying '-f help' on the command line.
While at it, simplify the code a bit, indent the output and eliminate an
extra blank line at the beginning.

Signed-off-by: Stefan Raspl <raspl@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>