Fixed handling of defaults and nodefaults in channel lists

[jlstevens]

Fix for the issue described in https://github.com/Anaconda-Platform/anaconda-project/pull/387 and https://github.com/Anaconda-Platform/anaconda-project/issues/388.

In short:

• The defaults channel was implicitly picked up from the .condarc
• nodefaults was ignored by anaconda-project (though it is respected by conda itself)
• The latest anaconda-project version now (correctly) ignores the ~/.condarc which has implications for backwards compatibility.

This PR attempts to fix this issue as follows:

• Make defaults explicit everywhere by appending it to the channel list if it is not stated. This should be backwards and forwards compatible with anaconda-project.
• Remove any instances of nodefaults, making sure defaults appears at the end of the list and noting that the intention was to avoid using defaults in a comment.

I believe this should fix compatibility but this PR has the possibility of breaking lots of things so please make sure you agree with this strategy @jbednar @maximlt !

[jlstevens]

Note: A separate PR should go through the projects trying to use nodefaults with the dev version of anaconda-project that actually respects it, to see if those projects actually function without defaults.

Also, I believe these changes shouldn't require relocking everything but I will have to double check.

[jlstevens]

Tests currently failing due to carbon flux not having test data. I'll have a look into this shortly.

[maximlt]

I totally approve this approach.

Note that you won't be able to build many examples, even before anaconda-project 0.11 they were mostly all broken. I have to resume the work on fixing that.

Tests currently failing due to carbon flux not having test data. I'll have a look into this shortly.

That sounds strange. For reference here's a table that sums up what data the projects need/use: https://github.com/pyviz-topics/examples/issues/202#issuecomment-1166689039

Also and seems to be of importance, anaconda-project is pinned to an older version in the ecosystem_setup command:

https://github.com/pyviz-topics/examples/blob/10772f10bc5e8dfd7c3bd8a894d372135176b39a/dodo.py#L17-L23

[jlstevens]

... Also and seems to be of importance, anaconda-project is pinned to an older version in the ecosystem_setup command

Well spotted!

That said, this pin is for the CI infrastructure associated with this repo, this PR as a whole is for users who may install any version of anaconda-project they want to try running these projects locally. Knowing the anaconda-project version is useful though, to debug any issues cropping up due to channel behavior.

[maximlt]

Also, I believe these changes shouldn't require relocking everything but I will have to double check.

I believe projects don't need their lock to be updated to run, but I also believe users will get a warning. I think for now it's fine and will go ahead and merge. Thanks Jean-Luc!