Split replaceAccount from addAccountToCache
Summary:
We were accidentally overwriting first account in the model with
currently logged in user after polling AccountsService
BUG: 336994
Test Plan: check if kcmshell5 user_manager lists mutliple users on cold boot
Reviewers: Plasma, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: davidedmundson, ngraham, rdieter, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D12837