dist/ami: follow rpm output dir path change
dist/ami: follow rpm output dir path change

CentOS mock support on build_rpm.sh changed rpm output directory, so follow it.

Fixes #2406

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>
Message-Id: <1495573343-13912-1-git-send-email-4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

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