Add a good test for QeAppWorkChain

[superstar54]

The old unit test uses a regression test on the final builder generated by the workchain. This is not a good design. Because the plugins depend on other packages, like aiida-quantumespresso, aiida-vibroscopy, and aiida-muon. Thus, the final builder also depends on those packages. In the latest work, we want to bump aside-quantum espresso to 4.5 and aside-core to 2.5, and the test failed because different aiida-quantumespresso produce different builder files.

In #644, I replaced the regression test using the ui_parameters generated by the app. This ui_parameter is the most important parameter. It contains all the information on the job, and one can use it to recreate the whole qeapp instance.

However, we still need a test on the QeAppWorkChain. The test should ideally only focus on the functionality of WorkChain itself.

For tests on the sub-WorkChains, which are related to the built-in plugins (bands, pdos, etc), one should add separate test files. In this way, the tests is clear and modularized.