Do not replace dots with underscores in topic names when constructing path

Some of our topic names contain dots. When generating the path,
Camus replaces all dots in a topic with underscores. This complicates our
migration away from Albert to Camus. Hence let's stop doing this.

In general, there has been a discussion in the Kafka community whether
dots, underscores and dashes should be banned from topic names as
it complicates writing JMX / Mbeans based monitoring tools for Kafka. The
current consensus seems to be that dots, underscores and dashes are okay.

See:
http://search-hadoop.com/m/4TaT4SHanu1&subj=Re+MBeans+dashes+underscores+and+KAFKA+1481
http://search-hadoop.com/m/4TaT4Jf1Jz1&subj=Re+Need+Document+and+Explanation+Of+New+Metrics+Name+in+New+Java+Producer+on+Kafka+Trunk
https://issues.apache.org/jira/browse/KAFKA-1481