kvm tools: Free vcpu array on shutdown

kvm tools: Free vcpu array on shutdown

This patch silences the following harmless warning to reduce valgrind noise:

  ==5529== 864 bytes in 3 blocks are possibly lost in loss record 39 of 48
  ==5529==    at 0x4A04B84: calloc (vg_replace_malloc.c:467)
  ==5529==    by 0x3DE6410D44: _dl_allocate_tls (in /lib64/ld-2.14.so)
  ==5529==    by 0x3DE70082F5: pthread_create@@GLIBC_2.2.5 (in /lib64/libpthread-2.14.so)
  ==5529==    by 0x405755: kvm_cmd_run (builtin-run.c:1169)
  ==5529==    by 0x40D47D: handle_command (kvm-cmd.c:84)
  ==5529==    by 0x3DE682139C: (below main) (in /lib64/libc-2.14.so)

Signed-off-by: Pekka Enberg <penberg@kernel.org>