ACL incorrectly creates ACL users

[danielmai]

Same as #135, but for users.

Steps to reproduce:

1. Run Dgraph cluster with ACLs enabled
2. Login as groot
3. Add a ACL user called "aUser"
4. Query for the group with the CLI tool:

$ dgraph acl info -u aUser
[Decoder]: Using assembly version of decoder

Running transaction with dgraph endpoint: 127.0.0.1:9080
Current password for groot:
Login successful.
Unable to show info: The user "aUser" does not exist.

Although Ratel says there's a user, it's not detected via the CLI tool.

[paulftw]

Fixed in master, new build is out.
Please re-open if you see this problem again