Cleanup configure_polaris_envs.py and deploy/shared.py

[altheaden]

This PR includes some general cleanup that I did in configure_polaris_envs.py and deploy/bootstrap.py, as well as a slight change to the commands which install mache. The cleanup I did consisted of the following:

• Privatized all applicable methods
• Re-ordered some methods
• Narrowed the scope of some try/catch blocks (such as catching a FileNotFound error instead of a more general OSError)
• Removed some unnecessary try/catch blocks (in the case of makedirs() which has a built-in FileExistsError check)

The installation of mache now calls upon a new file, deploy/spec-bootstrap.txt instead of listing mache's dependencies directly in the configure script. This change is both to make the script more modular and to make updating this list easier.

Checklist

• Testing comment in the PR documents testing used to verify the changes

[altheaden]

Testing

I tested this branch by creating a new polaris environment. Everything, as far as I can tell, went smoothly.

[xylar]

@altheaden, this looks excellent apart from one small thing to fix up. Once that's fixed, I'll test deployment both with the mache package from conda-forge and the local_mache cloned from a fork and branch.

[xylar]

@altheaden, other than my comment on the comment (how meta!) above, everything looks good by inspection. I'll do the tests I said it'd do and approve unless I run into any trouble.

[xylar]

I was able to create a polaris conda environment and activation script both with and without the --mache_fork/--mache_branch options. I don't think any further testing is needed for this PR.

Thanks for working on this, @altheaden!

[altheaden]

@xylar sounds great! I'll update that comment and then merge.