Rework the bootstrapper, add CoreOS etcd support

[karalabe]

The bootstrapper is one of the oldest components of the system and should really be rewritten. As part of that effort, I'd also like to add seamless coreos/etcd integration to take advantage of its discovery service if available. Although this is not really a necessity per se, but it's fairly simple to do and could make converging on CoreOS clusters extremely fast.

For details, please see the below discussions:

• https://groups.google.com/forum/#!topic/project-iris/tbCnM7u-Lw4
• https://groups.google.com/forum/#!topic/coreos-dev/qU1EbNWfDYQ

[coopernurse]

Excellent!

[karalabe]

I've reworked mostly the bootstrapper. It should theoretically take into accound local etcd instances to use as seed servers. Couple issues currently:

• Rate limiting is missing. I've yet to include a proper one. Currently one IP is probed/100ms. I'd like to replace this mechanism with a token bucket + an additional rate control from the upper layer pastry. This will probably be done in two phases, but enough to say that currently the bootstrapper is not working as intended until a proper rate limiter is in place.
• There is a bug in the pastry implementation if the bootstrap rate is too high. Tests begin failing if I probe 1IP/10ms (probably the same IPs get found multiple times and there's some race condition or something similar). This should also be sorted out before this issue can be closed or next version released.

[coopernurse]

Great, does this require any user configuration, or does it look for etcd on localhost:4001?

I wonder if we need to make this etcd endpoint configurable. With CoreOS/Docker I believe we'd want to connect to etcd running on the CoreOS host.

[karalabe]

Localhost 7001 (and the newly allocated IANA port), both IPv4 and 6. I don't think a configuration is warranted. I see no reason for people to override the etcd ports, especially if running stock CoreOS on cloud machines.