Fixing a bug in test_insert that was inserting dummy records in tinytable for text/codec

Change-Id: I3e7ac5cd97de6ff4cd0eab411ac4ed4ff6c77508
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3751
Reviewed-by: Ippokratis Pandis <ipandis@cloudera.com>
Tested-by: jenkins