Add logic to set the active install tree

lib/spack/spack/package.py

@@ -1492,6 +1492,17 @@ def do_install(self, **kwargs):
         dirty = kwargs.get('dirty', False)
         restage = kwargs.get('restage', False)
         install_global = kwargs.get('install_global', False)
+        upstream = kwargs.get('upstream', False)
+
+        # Install Package to Global Upstream for multi-user use
+        if install_global:
+            global_root = spack.config.get('upstreams')['global']['install_tree']
+            global_root = spack.util.path.canonicalize_path(global_root)
+            spack.config.set('config:active_tree', global_root)
+        elif upstream:
+            raise NotImplementedError
+        else:
+            spack.config.set('config:active_tree', spack.config.get('config:install_tree'))
 
         # For external packages the workflow is simplified, and basically
         # consists in module file generation and registration in the DB