Getting an error while registering a host using activation key with system purpose attributes. Even though there is an error, the host gets registered with the activation key successfully.

Steps to reproduce the bug:

1. Create an activation key with system purpose attributes.
2. Register a host using this activation key with the following command.
subscription-manager register --org "Default_Organization" --activationkey "keyname"
3. Getting the following error -

HTTP error (500 - Internal Server Error): Required lock is already taken by other running tasks.
Please inspect their state, fix their errors and resume them.

Required lock: update
Conflicts with tasks:
- http://centos7-katello-devel.swetha.example.com/foreman_tasks/tasks/0f9577a7-4e2d-469b-955f-60891182262b