Fix restaging of resources (#5681)

Part of the resource staging process is to place downloaded/expanded
files in the root stage. This was not happening when a resource stage
was restaged.

lib/spack/spack/stage.py

@@ -526,8 +526,18 @@ def __init__(self, url_or_fetch_strategy, root, resource, **kwargs):
         self.root_stage = root
         self.resource = resource
 
+    def restage(self):
+        super(ResourceStage, self).restage()
+        self._add_to_root_stage()
+
     def expand_archive(self):
         super(ResourceStage, self).expand_archive()
+        self._add_to_root_stage()
+
+    def _add_to_root_stage(self):
+        """
+        Move the extracted resource to the root stage (according to placement).
+        """
         root_stage = self.root_stage
         resource = self.resource
         placement = os.path.basename(self.source_path) \
@@ -535,12 +545,9 @@ def expand_archive(self):
             else resource.placement
         if not isinstance(placement, dict):
             placement = {'': placement}
-        # Make the paths in the dictionary absolute and link
+
-        for key, value in iteritems(placement):
         target_path = join_path(
             root_stage.source_path, resource.destination)
-            destination_path = join_path(target_path, value)
-            source_path = join_path(self.source_path, key)
 
         try:
             os.makedirs(target_path)
@@ -550,8 +557,11 @@ def expand_archive(self):
             else:
                 raise
 
+        for key, value in iteritems(placement):
+            destination_path = join_path(target_path, value)
+            source_path = join_path(self.source_path, key)
+
             if not os.path.exists(destination_path):
-                # Create a symlink
                 tty.info('Moving resource stage\n\tsource : '
                          '{stage}\n\tdestination : {destination}'.format(
                              stage=source_path, destination=destination_path