tools/kvm_stat: use a namedtuple for storing the values

tools/kvm_stat: use a namedtuple for storing the values

BugLink: http://bugs.launchpad.net/bugs/1734130
Use a namedtuple for storing the values as it allows to access the
fields of a tuple via names. This makes the overall code much easier
to read and to understand. Access by index is still possible as
before.

Signed-off-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>
Tested-by: Stefan Raspl <raspl@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 006f1548ac13d67d21865416a0f4e8062df1a85f)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>