Fix a bug in the account chooser where relaunching an in-progress flow

results in a blank screen.

The fix involves making the first activity just call the account
type chooser to get the account type to add, rather than having
the account type chooser also kick off the AccountManager.addAccount()
request itself. Instead the first activity will get the type
back and then call AccountManager.addAccount()

Bug: 5346810
Change-Id: I4a0cf2370971b98f8ee0910f5401d97e999e546b