reported here: http://www.redhat.com/archives/libvir-list/2014-November/msg00327.html

I could have just remove bool supportMaxOptions variable, but
if I had do this, we could not check anymore if the nparams variable is
superior to QEMU_NB_BLOCK_IO_TUNE_PARAM_MAX.

v2: change following this proposal:
http://www.redhat.com/archives/libvir-list/2014-November/msg00379.html