tests/test-classifier: Properly use ovsrcu_postpone.
Following patches add stricter checks of RCU memory management of
rules removed from a classifier. This patch properly postpones
freeing of 'struct cls_rule's that have been removed from a
classifier.
Also remove all the rules from classifier before destructing it in
test_rule_replacement().
Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com> Acked-by: Ben Pfaff <blp@nicira.com>