cgrulesengd enters an infinitive loop and cases high cpu usage with deleted users

Issue

• When a user account is deleted from the LDAP directory, but that user is still logged in to a server and starts a process after being deleted, both sssd and cgrulesengd start showing high cpu usage.
• This can be solved by restoring the user account, or by ending all the user's processes and restart cgred.
• It occurs whenever a user is deleted who still has active sessions and starts processes after being deleted.
• In our case we use LDAP, but the issue is reproducible with local accounts
• See cgrulesengd and sssd_nss consume cpu >50% until cgred restart (once all process belonging to the deleted user are finished)
• It happens at different times, if the circumstances are 'right', i.e. if a user is deleted and then processes are started with that user.
• Once it happens, it doesn't stop until the user is restored, or until the processes are finished and cgred is restarted.