dist: fix upstart script to make it able to start/stop correctly
dist: fix upstart script to make it able to start/stop correctly

Scylla is not "daemon" (witch forks twice), but it can be "fork" (forks once) when we don't use "exec" to call startup scripts.
Fixes #495

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,raphaelsc/scylla,duarten/scylla,kjniemi/scylla,raphaelsc/scylla,kjniemi/scylla,duarten/scylla,kjniemi/scylla,duarten/scylla,raphaelsc/scylla