storage: treat return value from ops->destroy as int
storage: treat return value from ops->destroy as int

r->ops->destroy() returns an int, -1 on error.
When assigned to a bool, this becomes true and hides errors.

Signed-off-by: Michael McCracken <af940a25c3809a29235b8e34c90fd6fdacecf6b2@cisco.com>

hallyn/lxc,hallyn/lxc,thmo/lxc,thmo/lxc,ss1h2a3tw/lxc,ss1h2a3tw/lxc,ss1h2a3tw/lxc,caglar10ur/lxc,thmo/lxc,caglar10ur/lxc,hallyn/lxc,caglar10ur/lxc