Fix csv metrics documentation. Directory creation

When the Metric's CSV reporter is enabled, it doesn't write to a file, but
instead writes a series of files to a specified directory. This commit fixes
all references of the single file notion.

This commit also creates the CSV reporter directory if it doesn't already
exist on start up. An appropriate test was created to confirm behavior.
Create parent directories and fail fast
Appease FindBugs with mkdirs return value
Merge pull request #583 from nickbabcock/csv-fix

Fix csv metrics documentation. Directory creation