Restructure tests

[mark-henry]

expected: I should be able to clone the repository and implement the practice test, with minimal work that does not imitate the work I have to do for the real GCF
actual: I had to get the tests set up, there was output like "uploaded at filename.txt" that my code was expected to return, expected output did not conform to the specification (for example, the spec says that "get" should return only the file size) and in general it was too dissimilar from the real GCF environment

I have rewritten the tests so that the test-taker can just get straight to work on their implementation! :)

I have also restructured them to be easier to read: each command is now directly paired with its expected output.

[ludomitch]

Even in these proposed changes, it's still not testing what the functions are supposed to do. Most asserts are if the function returns None. Not for example, if it has actually stored a file. Or asserting a runtime exception if the file already exists.

I imagine the repo is still in progress. @PaulLockett ?