In 0088fb45 I changed the management daemon's startup
script from a symlink to a Python script to a bash script that activated the new virtualenv
and then launched Python. As a result, the init.d script that starts the daemon would
write the pid of bash to the pidfile, and when trying to kill it, it would kill bash but
not the Python process.

Using exec to start Python fixes this problem by making the Python process have the pid
that the init.d script knows about.

fixes #1339