Fix various problems with SyncManagerAccountTests

1.  Destructive of existing user accounts in device
2.  Can get confused (miscounting) due to existing user accounts
3.  Cleaned up use of context and mock context
4.  Disallow account backup and account security updates when testing
5.  Make account manager removeAccount() calls blocking, so the test
    does not proceed until the accounts are really deleted.

Bug: 2454870
2 files changed