We currently don't have a simple mechanism to configure CuratorFramework's session and connection timeout.
Since Curator 3.x users can affect how Curator handles re-connection, since the meaning of LOST was changed.
In 3.x when the "Disconnected" is received Curator starts an internal timer.
When the timer passes the negotiated session timeout Curator calls `getTestable().injectSessionExpiration()`
and posts a LOST state change.
In Curator 4.x the session timeout defaults to 60 seconds and the connection timeout to 15 seconds.
Ref:
```
private static final int DEFAULT_SESSION_TIMEOUT_MS = Integer.getInteger("curator-default-session-timeout", 60 * 1000);
private static final int DEFAULT_CONNECTION_TIMEOUT_MS = Integer.getInteger("curator-default-connection-timeout", 15 * 1000);
```
Proposed Solution
=================
Offer a mechanism to configure the session and connection timeout and
establish a mechanism to be able to customize the `CuratorFramework` for
future-proving.
We could avoid having two more properties, the session and connection timeouts, as part of `ZookeeperProperties` and
let users define them on their `CuratorFrameworkCustomizer`. The current rational is that consolidating this two
configuration properties as part of the `spring.cloud.zookeeper` configuration namespace is valuable and simplifies
their usage.
Additional Context
==================
> Curator will set the LOST state when it believes that the ZooKeeper session has expired.
> ZooKeeper connections have a session. When the session expires, clients must take appropriate action.
> In Curator, this is complicated by the fact that Curator internally manages the ZooKeeper connection.
> Curator will set the LOST state when any of the following occurs:
> a) ZooKeeper returns a Watcher.Event.KeeperState.Expired or KeeperException.Code.SESSIONEXPIRED;
> b) Curator closes the internally managed ZooKeeper instance;
> c) The session timeout elapses during a network partition. It is possible to get a RECONNECTED state after
> this but you should still consider any locks, etc. as dirty/unstable.
Ref. [Curator Errors](https://curator.apache.org/errors.html)
Warning: Curator 4.0.1 is affected by [CURATOR-460: Timed tolerance for connection suspended leads to simultaneous leaders](https://issues.apache.org/jira/browse/CURATOR-460). This was addressed in `4.1.0`.
Additional references:
=====================
* [TN14: ZooKeeper's Session Handling](https://cwiki.apache.org/confluence/display/CURATOR/TN14)
* [CURATOR-460](https://issues.apache.org/jira/browse/CURATOR-460)
* [Curator Errors](https://curator.apache.org/errors.html)
fixes gh-244
This commits adds the option to define a Curator `TracerDriver`, which
if available, will be used in the CuratorZookeeperClient wrapped inside the
CuratorFramework.
Fixes gh-241
Fixes gh-242
