murmur3_partitioner: Convert maximum_token to sstring
murmur3_partitioner: Convert maximum_token to sstring

This patch ensures we can convert the maximum_token to an sstring.
For Cassandra, the minimum and maximum tokens have the same
representation. So, we use the string representation of the
maximum_token for the maximum_token.

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

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