sessions: allow passing zero lockDelay

[shdown]

Consul’s docs are inconsistent about this:

https://www.consul.io/docs/internals/sessions.html

While the default is to use a 15 second delay, clients are able to disable this mechanism by providing a zero delay value.

https://www.consul.io/api/session.html#lockdelay

LockDelay (string: "15s") - Specifies the duration for the lock delay. This must be greater than 0.

And consul has a couple of issues open about this:

• https://github.com/hashicorp/consul/issues/4508
• https://github.com/hashicorp/consul/issues/1077

But, surprisingly, Consul 1.5.0 understands lockDelay=0 as expected, that is, disables the lock delay mechanism for the session.

[oliora]

Nice catch!