tests: Don't depend on partition_key representation
tests: Don't depend on partition_key representation

Representation format is an implementation detail of
partition_key. Code which compares a value to representation makes
assumptions about key's representation. Compare keys to keys instead.
Message-Id: <84635af46cd0104779488904f4c139396df1960f@scylladb.com>

scylladb/scylla,avikivity/scylla,kjniemi/scylla,kjniemi/scylla,duarten/scylla,duarten/scylla,duarten/scylla,scylladb/scylla,raphaelsc/scylla,raphaelsc/scylla,kjniemi/scylla,avikivity/scylla,raphaelsc/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla