virttest.test_setup: Add some hugepage related config params

Alexander reported some problems running virt test on some
low memory PPC systems w.r.t. hugepages setup. In order to
make it easier to run virt-test without local code changes,
turn the QEMU memory overhead and whether to dealocate
huge pages something configurable.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>