dist/common/scripts: use out() to run perftune.py
dist/common/scripts: use out() to run perftune.py

perftune.py executes hwloc-calc, the command is now provided as
relocatable binary, placed under /opt/scylladb/bin.
So we need to add the directory to PATH when calling
subprocess.check_output(), but our utility function already do that,
switch to it.

Fixes #4443

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>
Message-Id: <20190418124345.24973-1-4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

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