[0.11] CREATE RETENTION POLICY and CREATE CONTINUOUS QUERY are not idempotent

[rkuchan]

• CREATE RP doesn't give an error if I create the exact same RP or if I create an RP with the same name but with a different DURATION:

> create retention policy blah on telegraf duration 1d replication 1
> show retention policies on telegraf
name       duration    replicaN    default
default    0           1           true
blah       24h0m0s     1           false

> create retention policy blah on telegraf duration 1d replication 1
> create retention policy blah on telegraf duration 2d replication 1
> show retention policies on telegraf
name       duration    replicaN    default
default    0           1           true
blah       24h0m0s     1           false

• CREATE CQ gives an error if I create the exact same CQ and if I create a CQ with the same name but with a different GROUP BY time interval:

> create continuous query new on telegraf begin select mean(usage_idle) into new from cpu group by time(5m) end
> show continuous queries
name: _internal
---------------
name    query


name: new
---------
name    query


name: telegraf
--------------
name    query
new     CREATE CONTINUOUS QUERY new ON telegraf BEGIN SELECT mean(usage_idle) INTO telegraf."default".new FROM telegraf."default".cpu GROUP BY time(5m) END

> create continuous query new on telegraf begin select mean(usage_idle) into new from cpu group by time(5m) end
ERR: continuous query already exists
> create continuous query new on telegraf begin select mean(usage_idle) into new from cpu group by time(6m) end
ERR: continuous query already exists

• CREATE USER doesn't give an error if I create the same user with the same password but does give an error if I create the same user with a different password:

> create user regan with password 'regan' with all privileges
> create user regan with password 'regan' with all privileges
> create user regan with password 'blueberries' with all privileges
ERR: user already exists
> show users
user    admin
regan   true