Testing: set more locale-globals in testing-script.

When testing Python modules, passing option --lang should also
set the global 'locale' (to a BCP47 string, but hey) like it
already sets localeConf.LANG.

src/modules/testmodule.py

@@ -88,6 +88,7 @@ def main():
     libcalamares.globalstorage = libcalamares.GlobalStorage(None)
     libcalamares.globalstorage.insert("testing", True)
     if args.lang:
+        libcalamares.globalstorage.insert("locale", args.lang)
         libcalamares.globalstorage.insert("localeConf", {"LANG": args.lang})
 
     # if a file for simulating globalStorage contents is provided, load it