domtop: Properly free cpu status
    
    So, in the example the cpu stats are collected within a function
    called do_top. At the beginning of the function we ask the daemon for
    how much vCPUs can we get stats, and how many stats for a vCPU can we
    get. This is because it's how our API works - users are required to
    preallocate a chunk of memory for the results. Now, at the end, we try
    to free the allocated array, but we are not doing it correctly.
    There's this virTypedParamsFree() function which gets a pointer to the
    array and the length of the array. However, if there was an error in
    getting vCPU stats we pass a negative number instead of the originally
    computed value. This flaw results in SIGSEGV:
    
    libvirt: QEMU Driver error : Requested operation is not valid: domain is not running
    ERROR do_top:333 : Unable to get cpu stats
    ==29201== Invalid read of size 4
    ==29201==    at 0x4F1DF8B: virTypedParamsClear (virtypedparam.c:1145)
    ==29201==    by 0x4F1DFEB: virTypedParamsFree (virtypedparam.c:1165)
    ==29201==    by 0x4023C3: do_top (domtop.c:349)
    ==29201==    by 0x40260B: main (domtop.c:386)
    ==29201==  Address 0x131cd7c0 is 16 bytes after a block of size 768 alloc'd
    ==29201==    at 0x4C2C070: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
    ==29201==    by 0x401FF1: do_top (domtop.c:295)
    ==29201==    by 0x40260B: main (domtop.c:386)
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>