Testsuite: check actual_prof_file only when needed

Might be a little faster. Avoids testing for #6113 (.prof file not
written when process is killed with any signal but SIGINT) for tests
that don't have a .prof.sample file (which is almost all of them) when
running the profiling ways.
Tests that were failing because of #6113: T8089, overflow1, overflow2 and
overflow3.