(#20447) Wait for server to shutdown before exiting daemon

Previously, if the filetimeout was set to 0 and the puppet master was
run, the master would exit immediately. This was caused by the scheduler
having nothing to do and the new logic for it causes it to stop running
at that point (because once there is nothing to do, there is also no
chance that something will cause it to having something to do). There
was a slightly wrong assumption that was being made for that logic: the
scheduler is in control of all activity in the daemonized process. This
is not the case.

The daemon has 3 parts to it:
  * configuration reparse
  * agent runs
  * server control

The server does not take part in the scheduler inside the daemon. It is
assumed to be a separate thread/process, which the daemon will kick off
when it starts, and stop when the daemon is told to stop. When the
"start" method of the daemon exits, the daemon itself exits and the
server will be required to shut down.

There are 2 ways that could be used to solve this problem: have the
scheduler sit in a busy loop (or sleep forever) when it has nothing to
do, or wait for the server to finish before the daemon considers itself
done. This commit uses the latter option.

The new code will wait for the server to finish before the Daemon#start
method returns. This makes the dependency explicit rather than hidden in
an infinite loop in the scheduler.
Merge pull request #1627 from zaphod42/issue/stable/20447-filetimeout0-causes-master-to-exit

(#20447) Wait for server to shutdown before exiting daemon