MockModuleBuilder: move generated artifacts to the final directory, instead of copying them

There's no good reason to have artifacts in both the thread-specific results directory
and in the main results directory, so just move them across instead of copying them.

https://pagure.io/fm-orchestrator/issue/591

module_build_service/builder/MockModuleBuilder.py

@@ -27,7 +27,6 @@ import os
 import koji
 import kobo.rpmlib
 import modulemd
-import shutil
 import yaml
 import threading
 
@@ -382,7 +381,7 @@ mdpolicy=group:primary
 
         # Copy files from thread-related resultsdire to the main resultsdir.
         for name in os.listdir(resultsdir):
-            shutil.copyfile(os.path.join(resultsdir, name), os.path.join(self.resultsdir, name))
+            os.rename(os.path.join(resultsdir, name), os.path.join(self.resultsdir, name))
 
         # We return BUILDING state here even when we know it is already
         # completed or failed, because otherwise utils.start_build_batch