(#12349) Add module dependency errors to module list output

There was already a validate_dependencies method on the Puppet::Module
class, but it didn't do anything since it never actually read the
dependency info from the module metadata.

This commit adds a method to replace that, but it doesn't raise if
dependencies are unsatisfied. This allows us to output the dependency
problems when puppet module list is called.

This also adds basic acceptance tests for the list command.