factor out function for getting top level directory of cloudinit

[holmanb]

Add a test helper to get top level directory

Many tests need to get the location of files & dirs within the cloud-init
project directory.

Tests implement this in various different ways, and often those ways
depend on the current working directory of the pytest invocation.
Create helper functions (and tests) that gets the path of the top
directory or any sub directory under the top directory. This function
does not depend on the environment.

Additional Context

• This is not a very high value refactor, but not being able to run pytest wherever I please has been bugging me.
• It should also makes a common task less slightly less error prone and tedious.
• I'm sure that I missed tests.
• The tests I converted were unittests that fail when running pytest in a subdirectory.

[holmanb]

Setting the pythonpath environment variable in subp didn't seem to work. That would have been cleaner, but this works too.

[smoser]

you probably want to prepend, not append. The right 'cloudinit.subp' to import is the one in the top level dir, if there were others in the path for some reason then you'd get the wrong one.

that said, '' is (I think) usually the first token of sys.path, which is why this worked before. So I don't really think you have to change anything unless the intent is to execute these tests with some other working directory.

[holmanb]

Good call @smoser. Thanks!

[TheRealFalcon]

I like the overall approach...just some inline questions about the function implementation.

Also, I think test_schema.py, line 53 needs this too. It currently looks like
files = list(Path("../../cloudinit/config/").glob("cc_*.py"))
which doesn't work for me since I'm not running pytest from that directory. I have it replaced locally with

    files = list(
        (
            Path(__file__).parent.parent.parent.parent / "cloudinit" / "config"
        ).glob("cc_*.py")
    )

which is much less nice than using this would be.

[TheRealFalcon]

Thanks!