Support multiple case directories for one environment

[jiacai2050]

Describe This Problem

In current implementation, there is only one case directory allowed for one environment, although this works, but this makes it awkward to share cases between multiple environment.

Proposal

Support multiple case directories

Additional Context

Another solution to this is symlinks, although this works, but I think it's a little ugly.

[jiacai2050]

Symblinks support has been merged. Other solution is to use setup two projects with same case dir, but only one env and each project has different result_extension, in this way users can reuse sql testcases, but output to different result file.