[TEST] Add unit/integration/end-to-end tests

[starbops]

Currently, the project lacks testing to protect the code. We need to add different levels of testing to ensure the code's robustness and quality. This is also a requirement before we can transfer the project to the KubeVirt organization according to the implementation phases of the design proposal.

P.S. This is a follow-up issue of #1.

[starbops]

I didn't notice that the linked PR #8 closed the issue automatically. I've added more tests in #29 and am still working on the e2e tests.

[starbops]

We still lack the e2e testing for the data plane, i.e., virtual machine interaction via IPMI (and Redfish, hopefully).