[CORE] vmm_scheduler: Sample time spend in processing interrupts

Sampling time spend in processing interrupts is very important
for VCPU load balancer and IRQ balancers hence this patch improves
our existing idle time sampling to sample both idle time and
irq time.

In addition, to above this patch extends "host cpu info" command
to show percent time spend by each host CPU in processing interrupts.

Signed-off-by: Anup Patel <anup@brainfault.org>