In order to test the output from a test command, the commandOutput
function exists in the command_test.go file.
Since its behaviour is linked to the test meta that we produce in the
test_utils.go file, we move it there, and rename it to
`GetStdoutAndErrFromTestMeta' to make it clearer what to expect from it.
* allowing to set shell env vars from a key/value map.
* tests
This new map will work alongside the `environment_vars` but it allows using a
datasource value seamlessly. At validation, and because `environment_vars` was
an array of strings containing `KEY=value`, using datsources would not work,
because these values are not known yet and would evaluate to `<unknown>`. With
this, the value and the key can be unknown and will validate correctly for
datasources.
