PE should support multi column family read and write cases

PerformanceEvaluation has a --columns parameter but this adjusts the number of distinct column qualifiers to write (and, with --addColumns, to add to the scan), not the number of column families.

We need something like a new --families parameter that will increase the number of column families defined in the test table schema, written to, and included in gets and scans. Default is 1, current behavior.