[zookeeper-mt] Add new port

[SamuelMarks]

Apache ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services.

EDIT: WOOT: 7000!

[dan-shaw]

@SamuelMarks Thanks for the PR! I've made some changes:

1. Added support for zookeeper_st shared library (it's the zookeeper[async] feature). However, by default zookeeper_mt is installed. I've also changed the name from zookeeper-mt to zookeeper since we now support both libraries.
2. I've made it into a static library since zookeeper doesn't support BUILD_SHARED_LIBS yet
3. I've also refactored some of the cmake

Let me know if I missed anything.

[dan-shaw]

Thanks for the PR!