cluster/local: support lock/unlock

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
tests/func: add nginx.conf

This is needed for later test cases to test http services. It is convenient to
include it in the tests and make tests self-contained.

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
tests/func: add 081 to test http service

Current master can pass it with local driver, but zk driver can't.

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
tests/func: add 082 to test http services with multiple servers

Current local deiver can pass it but zk can't

Signed-off-by: Liu Yuan <namei.unix@gmail.com>