[cassandra cassandra2 dynamodb hbase098 hbase10 jdbc s3] Fixing squid:S1481 - Unused local variables should be removed

Also fix a few README formatting issues.

        mvn org.apache.rat:apache-rat-plugin:0.11:check -D rat.numUnapprovedLicenses=5000

Replaces numeric status codes with a canonical set of Status objects,
each with a short name and description.
Bindings with more specific errors (e.g., timeouts) return additional
statuses.

This changes the default output from messages like:

   [UPDATE], Return=0, 511

To:

   [UPDATE], Return=OK, 511