virCapabilitiesInitCaches: Don't leak @cpus
    
    The @cpus is allocated by virFileReadValueBitmap() but never
    freed:
    
    ==21274== 40 (32 direct, 8 indirect) bytes in 1 blocks are definitely lost in loss record 808 of 1,004
    ==21274==    at 0x4C2E080: calloc (vg_replace_malloc.c:711)
    ==21274==    by 0x54BA561: virAlloc (viralloc.c:144)
    ==21274==    by 0x54BC604: virBitmapNewEmpty (virbitmap.c:126)
    ==21274==    by 0x54BD059: virBitmapParseUnlimited (virbitmap.c:570)
    ==21274==    by 0x54EECE9: virFileReadValueBitmap (virfile.c:4113)
    ==21274==    by 0x5563132: virCapabilitiesInitCaches (capabilities.c:1548)
    ==21274==    by 0x2BB86E59: virQEMUCapsInit (qemu_capabilities.c:1132)
    ==21274==    by 0x2BBEC067: virQEMUDriverCreateCapabilities (qemu_conf.c:928)
    ==21274==    by 0x2BC3DEAA: qemuStateInitialize (qemu_driver.c:845)
    ==21274==    by 0x5625AAC: virStateInitialize (libvirt.c:770)
    ==21274==    by 0x124519: daemonRunStateInit (libvirtd.c:881)
    ==21274==    by 0x554C927: virThreadHelper (virthread.c:206)
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>