improve potential memory access overflow risk for #104

[cuber]

1. because life cycle of cmcf is as long as the nginx worker, so updating this variable dynamically will case potential memory access overflow risk see the discussion alibaba/tengine#1133

2. completely test for the modules below tengine/ngx_http_upstream_check_module tengine/ngx_http_upstream_consistent_hash_module

3. seperate unit test cases files for different module