tests: fix bad format string syntax
tests: fix bad format string syntax

Some sprint() calls use the fmt language instead of the printf syntax. Convert
them all the way to format().

avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla