STORM-603 Log errors when required kafka params are missing

https://issues.apache.org/jira/browse/STORM-603

I was upgrading our topologies to storm-0.9.3 this [commit](https://github.com/apache/storm/commit/2596e335f27a57784a93a57823bd93dde587909f) introduced a change that threw me for a loop. When submitting my topology I got the following error.
```
[main] ERROR storm.kafka.DynamicBrokersReader - Couldn't connect to zookeeper
 java.lang.IllegalArgumentException: Don't know how to convert null to int
 	at backtype.storm.utils.Utils.getInt(Utils.java:301) ~[storm-core-0.9.3.jar:0.9.3]
 	at storm.kafka.DynamicBrokersReader.<init>(DynamicBrokersReader.java:47) ~[gambit-storm-threads-0.0.1-SNAPSHOT-jar-with-dependencies.jar:na]
 	at com.pearson.gambit.threads.storm.ThreadsTopology.main(ThreadsTopology.java:45) [gambit-storm-threads-0.0.1-SNAPSHOT-jar-with-dependencies.jar:na]
 Exception in thread "main" java.lang.RuntimeException: java.lang.RuntimeException: java.lang.NullPointerException
 	at storm.kafka.DynamicBrokersReader.getBrokerInfo(DynamicBrokersReader.java:81)
 	at com.pearson.gambit.threads.storm.ThreadsTopology.main(ThreadsTopology.java:48)
 Caused by: java.lang.RuntimeException: java.lang.NullPointerException
 	at storm.kafka.DynamicBrokersReader.getNumPartitions(DynamicBrokersReader.java:94)
 	at storm.kafka.DynamicBrokersReader.getBrokerInfo(DynamicBrokersReader.java:65)
 	... 1 more
 Caused by: java.lang.NullPointerException
 	at storm.kafka.DynamicBrokersReader.getNumPartitions(DynamicBrokersReader.java:91)
 	... 2 more 
```

It took me a while to figure out that this error stems from missing the `backtype.storm.Config.STORM_ZOOKEEPER_CONNECTION_TIMEOUT` property in the `conf` map provided to the `storm.kafka.DynamicBrokersReader` constructer. It would be nice to check the required configuration parameters and throw a RuntimeException if any are missing. 
This pull requests adds logging when required errors are missing.