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
I met a failure of reading hdfs files in broker load, the error message is unclear and
I spent a lot of time to locate the problem.
```
W0330 11:08:01.093812 2755268 broker_scan_node.cpp:364] Scanner[0] process failed. status=connect failed.
W0330 11:08:01.097682 2018787 fragment_mgr.cpp:234] Got error while opening fragment 712ae2b848324cb6-94a83d646173c1e9: Internal error: connect failed.
W0330 11:08:01.097702 2018787 tablet_sink.cpp:148] connect failed.
```
We should add more information when connect to hdfs failed.
