rgw/rgw_rados.h: use static_cast instead of c-style cast

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
RadosStriperImpl.cc: catch exception by reference

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
libcephfs/test.cc: fix use after free

Don't call ceph_shutdown() after ceph_release().

CID 1219651 (#1 of 1): Use after free (USE_AFTER_FREE)
  17. deref_arg: Calling ceph_shutdown dereferences freed
  pointer cmount.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>