Move tests to top-level

[sajith]

Part of #184. Changes:

• Moves fabrictestbed_extensions/tests/ to a top-level tests/ folder, and rearranges into a directory structure like so:

tests/
├── benchmarks
│   ├── gpu_tesla_t4_benchmark.py
│   ├── link_benchmark.py
│   ├── local_network_benchmark.py
│   ├── network_benchmark_tests.py
│   └── nvme_benchmark.py
├── integration
│   ├── abc_test.py
│   ├── component_tests.py
│   └── hello_fabric.py
└── unit
    ├── data
    │   └── dummy-token.json
    ├── __init__.py
    └── test_basic.py

The advantage of moving tests to top-level is that the wheel package will not have fabrictestbed_extensions.tests module. Top-level tests directory also won't be included in the wheel package. Tests are useful for developers of FABLib, but not so for the consumers of the wheel package.

• Adds a tox.ini, onto which we can add environments for running integration tests and benchmarks. I am still figuring out how to make them runnable. I suppose they are figure-outtable.
• The integration tests and benchmarks are not usable yet, and @kthare10 is of the opinion that they could simply be removed, and acceptance test notebooks could be re-purposed as FABlib integration tests. I am not so sure about removing the existing tests right now. I would like to try update them and make them useful, if possible, before abandoning them altogether. Either way I would like to do that in follow-up PRs after assessing their usefulness.

[coveralls]

Pull Request Test Coverage Report for Build 5447577478

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.0%) to 20.712%

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Totals
Change from base Build 5298386964:	1.0%
Covered Lines:	957
Relevant Lines:	4181

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💛 - Coveralls

[kthare10]

+1