Add new “daemon-util” script to start/stop Ganeti daemons

Until now, Ganeti started and stopped its own daemons using custom functions.
To start, the daemon was just executed and then sent the appropriate signals to
stop it again. Init scripts would have to pay attention to the PID file and
other things.

With this patch, a new script is added (“daemon-util”, installed in
$prefix/lib/ganeti/), centralizing the starting and stopping of daemons. The
provided example init script is adjusted to use this new script. Ganeti's code
no longer calls its own init script.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>