Don't copy symlinked folders

[Flamefire]

filetools.copy_dir directly calls shutil.copytree with symlinks=False by default which means that symlinks will be followed and their contents copied instead of the symlinks

Also many EasyConfigs use the parameter keepsymlinks which is also set to False by default and often forgotten. E.g. for the EasyBlocks MakeCp and Tarball

I propose to switch the default to copy symlinks as symlinks instead and not resolve them. This has the following benefits:

• Especially for Tarball I'd say the expectation is that the result is the same as when directly extracting the tarball to the destination
• It works more often. The current default may needlessly copy stuff or even result in full failures. Happened during installation of Spack which has a recursive symlink (due to some localization stuff)
• It works for absolute and broken (at install time) symlinks. I doubt we'd ever want to copy the contents of absolute symlinks, do we? And for broken ones they may be resolved later, e.g. to user home directories or similar

As an alternative and extension to #3784 I'd propose that if the directory tree to be copied contains symlinks, then an explicit choice must be made. I.e.

• keepsymlinks defaults to None
• copy_dir takes symlinks=None
• If the folder does not contain any symlinks then symlinks is set to any value by copy_dir
• Otherwise: if symlinks is None an error is thrown

This at least avoids mistakes by forgetting about that param and won't affect most installations.

[boegel]

@Flamefire I agree that we should switch to retaining symlinks rather than resolving them, but that's a change we can/should only make in EasyBuild 5.0 imho.