Fix resolved (template) values in case of failure

[Flamefire]

When the value cannot be resolved usually the original value is returned.
However if it contains % signs there will be an escape step and that escaped value is returned.

That makes it impossible to have values which can only later be resolved, like
cd %(startdir)s in extensions which would become
cd %%(startdir)s on the first resolve-attempt.

This is impossible to "undo" in the current framework hence we must take care of this case.

I also did some related changes:

• pylint detected some cases where dict.items should be used
• The escaping/unescaping of template values as documented in resolve_template was not tested

Recent actual failure was using cp %s %(builddir)s/archives as the extract command in a component. I'd argue that should work as expected although there is a workaround: Escaping the %(builddir)s template. But that kind of requires to know how many times EasyBuild will try to resolve templates.

[boegel]

@Flamefire The case from easybuilders/easybuild-easyconfigs#20119 that happens to work now should also be taken into account.
Although that happens to work by accident almost, can we somehow prevent from breaking that use case where %(builddir)s is being escaped to avoid trouble with the %s that accompanies it?

[Flamefire]

can we somehow prevent from breaking that use case where %(builddir)s is being escaped to avoid trouble with the %s that accompanies it?

I'm not sure we can and don't think we should. #4516 might also have avoided the issue we had as it avoids resolving where we can and allows failures at places where they might happen. Haven't checked but I guess there it won't try to resolve the extension values when reading them. And with this change it won't matter anymore how often EB tries to resolve templates until it succeeds: The value stays unchanged.

Additionally we have:

easybuild-framework/easybuild/framework/easyconfig/easyconfig.py

Line 2020 in ae29588

# '%%(name)s' -> '%%(name)s', and after templating with {'name':'x'} -> '%(name)s'

According to this no-one should expect that workaround to work, should they? And the idea was explicitly that things like %(builddir)s %s work, i.e. the %s is not tried to be resolved by EB during template steps, see the test for the single %s (which works now too): https://github.com/easybuilders/easybuild-framework/pull/4532/files#diff-bf1c3722aa26c6569dd59d4e4a92f16c88bf688276708beb9f09df6e40288713R3662

[boegel]

lgtm