[distcc] distcc cluster monitoring

[Dan Kegel]

Apologies if this is repetitive, but:

Currently, distccmon-text and its ilk let you monitor
your own jobs, but not the cluster as a whole.

lsdistcc is a handy commandline tool for pinging
all nodes of a distcc cluster to see which ones
are up.  It can be used when starting a Make run
to set DISTCC_HOSTS to exclude bad or overloaded hosts,
which is very nice.
However, for large installations, using lsdistcc in
this way doesn't scale terribly well.

I'm considering adding a server mode to lsdistcc so
it can act as an http server.   Then anyone who
would have run lsdistcc on their own can do something like
  wget -O- lsdistccserver1
to retrieve the list of currently-up server nodes.
To avoid adding a single point of failure, you can run several
of these servers, and query them in turn until you get
an answer, kinda like this:
   wget -O - -T 3 lsdistccserver1/hosts || wget -O - -T 3 lsdistccserver2/hosts

This will scale better (i.e. the distcc and dns traffic related
to monitoring will increase much slower with the number of
clients, and it should be less sensitive to DNS flakiness).

The lsdistcc server mode could also serve up reports of
various flavors, e.g. it could show which distcc nodes are
down.

Comments?
- Dan

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