Module builds now remember what module they reused for building.

There was a race condition, when 2 builds where build in the same time.
There was an issue that after one has finished the other reused the new build
for reuse and not the one it started with.

Ticket-ID: FACTORY-3862

Signed-off-by: Martin Curlej <mcurlej@redhat.com>

module_build_service/utils/reuse.py

@@ -85,8 +85,11 @@ def get_reusable_module(session, module):
     :param module: the ModuleBuild object of module being built.
     :return: ModuleBuild object which can be used for component reuse.
     """
-    mmd = module.mmd()
 
+    if module.reused_module:
+        return module.reused_module
+
+    mmd = module.mmd()
     # Find the latest module that is in the done or ready state
     previous_module_build = (
         session.query(models.ModuleBuild)
@@ -111,6 +114,9 @@ def get_reusable_module(session, module):
         log.info("Cannot re-use.  %r is the first module build." % module)
         return None
 
+    module.reused_module_id = previous_module_build.id
+    session.commit()
+
     return previous_module_build