librbd: parse args to ceph_test_librbd

Signed-off-by: Sage Weil <sage@inktank.com>
ceph_test_librbd: fix heap overrun

We are storing rbd_snap_info_t structs, not pointers to them.  But we
can also avoid the heap entirely.

This crashed pretty reliably on arm.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #754 from ceph/wip-test-librbd

fix ceph_test_lirbd crash
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>