Automated logviewer launch for 1.x

Automated logviewer launch on any worker hosts running Storm bits (1.x specific)
State of these logviewer daemons are tracked per host by stuffing state into ZooKeeper
Reconciliation is also implemented to ensure that logviewers are brought back alive if ever killed.

Wrapper around Apache Curator in order to interact with ZK
Can create, delete, and check for existence of nodes in ZK
Used to track which hosts are running logviewer daemons by tracking that state into ZK
Junit tests are written for this class

Added TimerTask to perform implicit reconciliation every 5 minutes
- Implicit reconciliation reconciles that state of every running task between the framework scheduler and master (sends update of task status to statusUpdate method in NimbusMesosScheduler)
launchLogviewer method called in allSlotsAvailableForScheduling loops through the existingSupervisors and schedules the logviewer daemon as Mesos tasks based on the offers available on each host
- Checks ZK if logviewer already running on the host which the supervisor is running on, as such, ensures that logviewer only runs on hosts with Storm bits

Updated statusUpdate method to look for logviewer tasks to check if they need to be relaunched
updateLogviewerState method updates the state of the logviewer task in ZK if needed
- reviveOffers if logviewer needs to be relaunched

Added new config called storm.logviewer.zookeeper.dir which allows you to configure under which "path" you want the logviewer state to be stored in ZK

mesos / storm