databases should always have a default retention policy

[beckettsean]

In 0.9.2 it is possible to drop the default RP, meaning all subsequent writes that don't explicitly specify an RP will fail.

> use test
Using database test
> show retention policies on test
name    duration    replicaN    default
default 0       1       true
foo 3h25m45.678s    1       false

> drop retention policy "default" on test

> show retention policies on test
name    duration    replicaN    default
foo 3h25m45.678s    1       false

> insert foo,bar=baz value=123
ERR: retention policy not found

It is not possible to remove the default setting from a retention policy except by explicitly declaring another policy the default. I think the only way to end up without one is to drop the current default RP.

[otoolep]

Should be fixed by #4053

[otoolep]

All fixed.