Description of problem:
When selecting a merge target, if the user signs into a google account that does not have an account on Zanata it should not prompt to create a new account.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Sign into Zanata with a google account
2. Go to Settings, and click Merge
3. Sign into a google account that is not related to the Zanata instance
Create new user is displayed
"Account not found" should show - it can't be merged if it doesn't exist.
If the user fills in the form and creates another user, they will be signed out of both accounts. Signing in to the original account and pressing merge again shows the "no such account" error.