Fix issue with saving admins before finishing loading.

Saving device policy managers settings to clear out
password stats was happening before initializing mAdminList
so could wipe active admins.

Test: manual - flash with N2G05C add google account with dmagent flash wth this fix, check dmagent is still an active admin, reboot check admin is still active.
Test: runtest -c com.android.server.devicepolicy.DevicePolicyManagerTest frameworks-services

Bug: 34277435
Change-Id: I13660b47f30e9aba001eb13f2e457c3b3f36da3e