* Replace use of `testChdir` with `t.Chdir`
* Update tests to use temporary directories with copied content, instead of using directories in the repo directly.
* Remove stacks copy of testChdir function
This has been replaced with t.Chdir from the standard library
* Replace remaining simple usage of testChdir
* Update guidance for using `tempWorkingDir`
* Replace use of testChdir in a function reused in a single test
* Update comments to no longer recommend using testChdir
* Remove testChdir function!
This commit makes several modifications to the modules command. It
downcases the field names in the resulting JSON string, adds a format
version to the result. The result of this command will now only contain
entries which have been declared in configuration, as opposed to the
internal manifest which shows all installed modules for a working dir.
