RP should not allow INF or 0 as a shard duration

[beckettsean]

Bug report

System info: [Include InfluxDB version, operating system name, and other relevant details]

InfluxDB 1.0.x

Actual behavior: [What actually happened]

CREATE RP and ALTER RP queries will accept INF as a valid duration, which should not be accepted, as shards must have an explicit end time. What ends up happening is the shards have a 1s duration, effectively meaning all data is dropped as soon as it is written.

Desired behavior:

Throw an error and reject the RP query.