There are 3 error code types in BE: OLAPStatus AgentStatus Status.
It is very confused and sometimes conflict during write code.
I will try to unify them to Status.
For the first, we need to make a parameter to discribe the data is local or remote.
At then, we need to support some basic function to support the operation for remote storage.
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`
1. Fix error class in start_fe.sh and start_broker.sh.
2. Add log4j2.xml in fe/src/test/resources/ to run fe ut without log4j warnings.
3. Reduce the test file size in be ut.
