Improve NoHostAvailableException error message
stress: optimize and add sync/async options

* use one generator per worker
* run async workers on a threadpool, don't block
Support null values in the query build

JAVA-105 #fixes
Add SSL support
Log a warning when schema agreement cannot be reached in 10 seconds
Ensure we don't overflow in ExponentialReconnectionPolicy

JAVA-107 #fixes
Make pom work on recent maven