perf kvm: Do guest-only counting by default

Make use of exclude_guest and exlude_host in perf-kvm to do only
guest-only counting by default.

Cc: Gleb Natapov <gleb@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
[ committer note: Moved perf_{guest,host} & event_attr_init to util.c ]
[                 so as not to drag more stuff to the python binding]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>