Fix assertion failure when checking named-checkconf version

Fix assertion failure when checking named-checkconf version

The dst_lib_destroy() should be called only if dst_lib_init() was called
before.  In named-checkconf, that is guarded by dst_cleanup variable
that was erroneously set to true by default.  Set the dst_cleanup to
'false' by default.

(cherry picked from commit c54880e3fad9f6c569de04fccf5489372b624311)