1. solved the previous delayed unit test file size is too large (1.7G+) and the unit test link time is too long problem problems
2. Unify all unit tests into one file to significantly reduce unit test execution time to less than 3 mins
3. temporarily disable stream_load_test.cpp, metrics_action_test.cpp, load_channel_mgr_test.cpp because it will re-implement part of the code and affect other tests
1. relocation R_X86_64_32 against `__gxx_personality_v0' can not be used when making a shared object; recompile with -fPIC
2. warning: the use of `tmpnam' is dangerous, better use `mkstemp'
3. Death tests use fork(), which is unsafe particularly in a threaded context. For this test, Google Test couldn't detect the number of threads.
In the past, when we want to modify some BE configs, we have to modify be.conf and then restart BE.
This patch provides a way to modify configs in the type of 'threshold', 'interval', 'enable flag'
when BE is running without restarting it.
You can update a single config once by BE's http API: `be_host:be_http_port/api/update_config?config_name=new_value`
* add authentication to DownloadAction
1. use cluster_id as token;
2. add dir limit, only files in data dir can be accessed.
* enable authentication in DownloadAction by default
