CREATE USER query fails if user already exists

[bbinet]

As stated on #5360 (comment) the if not exists behavior should now be the default for all create statements, but when I try to create a user that already exists with influxdb nightly build (version 0.11.0.n1456300834, branch master, commit e32e5ff, built 2016-02-24T08:01:27.779046), it does not work:

> CREATE USER u_a WITH PASSWORD 'u_a'
[query] 2016/02/24 13:32:37 CREATE USER u_a WITH PASSWORD [REDACTED]
[http] 2016/02/24 13:32:37 127.0.0.1 - root [24/Feb/2016:13:32:37 +0000] GET /query?db=_internal&epoch=ns&q=CREATE+USER+[REDACTED]+WITH+PASSWORD+%27[REDACTED]%27 HTTP/1.1 200 68 - InfluxDBShell/0.11.0.n1456300834 11a9392a-dafb-11e5-800d-000000000000 140.748357ms
ERR: user already exists

[bbinet]

I've just noticed the category/clustering label, but I think this issue is not related to clustering since the CREATE USER query failed for a standalone InfluxDB.

[e-dard]

FIxed via #6010