Refactor logging

[Marked as Major because it's highly visible in the logs, it's important to see pre-post options especially when dealing with reconfigutations during troubleshooting]
[Tested with the sample config template]

1. WARN msg is printed in the logs, when it shouldn't be a warning... maybe just INFO:
2012-04-24 19:56:59,370 (conf-file-poller-0) [WARN - org.apache.flume.conf.FlumeConfiguration$AgentConfiguration.validateSinks(FlumeConfiguration.java:591)] Sink: loggerSink

2. The initial (prevalidation) config should show the props that were read from the config file before validation, rather than showing an empty list.
2012-04-24 19:56:59,353 (conf-file-poller-0) [DEBUG - org.apache.flume.conf.FlumeConfiguration$AgentConfiguration.isValid(FlumeConfiguration.java:284)] Starting validation of configuration for agent: agent, initial-configuration: AgentConfiguration[agent]
SOURCES: {}
CHANNELS: {}
SINKS: {}

3. The final (post-validation) config should be pretty-printed, like the initial config. Currently it looks like this:
2012-04-24 19:56:59,389 (conf-file-poller-0) [INFO - org.apache.flume.node.nodemanager.DefaultLogicalNodeManager.onNodeConfigurationChanged(DefaultLogicalNodeManager.java:54)] Node configuration change:{ sourceRunners:{seqGenSrc=PollableSourceRunner: { source:org.apache.flume.source.SequenceGeneratorSource@450e790c counterGroup:{ name:null counters:{} } }} sinkRunners:{loggerSink=SinkRunner: { policy:org.apache.flume.sink.DefaultSinkProcessor@392d263f counterGroup:{ name:null counters:{} } }} channels:

}