tests/random-utils: make functions and variables inline
tests/random-utils: make functions and variables inline

random-utils.hh is a header which may be included in multiple
translation units so all members should be non-static inline to avoid
any duplication.

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