Fix error message displayed when Gerrit-init fails

The gerrit-init.py script in the gerrit-init container contained a bug
in an error message that was displayed, if the Gerrit-initialization
failed.

This change fixes the variable reference causing this bug.

Change-Id: I40b4057976a85a88433a291cf93ef8cd7c8f22bd

container-images/gerrit-init/tools/gerrit_init.py

diff --git a/container-images/gerrit-init/tools/gerrit_init.py b/container-images/gerrit-init/tools/gerrit_init.py
index 4b4b1c5..96d2114 100755
--- a/container-images/gerrit-init/tools/gerrit_init.py
+++ b/container-images/gerrit-init/tools/gerrit_init.py
@@ -57,7 +57,8 @@
   init_process = subprocess.run(command.split(), stdout=subprocess.PIPE)
 
   if init_process.returncode > 0:
-    print("An error occured, when initializing Gerrit. Exit code: ", exit_code)
+    print("An error occured, when initializing Gerrit. Exit code: ",
+      init_process.returncode)
     sys.exit(1)
 
 if __name__ == "__main__":