Handle certain errors in action=createaccount api module

Certain errors (user blocked, user doesn't have permission)
were causing uncaught exceptions to be thrown in this api module.
Try to check for those cases first. Also added some errors
to the possible error list.

Change-Id: Id86984ade23a818317b942de3e9cf0ccdb43fba7
Merge "Handle certain errors in action=createaccount api module"