Update buildslave.rst page for Buildbot 0.9.x

[zware]

In part, the whole page needs s/slave/worker/g; any links to the master page will be wrong, and there may be other updates necessary as well.

[levlaz]

@zware I would love to tackle this issue.

I ran linkcheck, and focused on the buildbot specific links.

buildbots.rst:48: [broken] http://buildbot.python.org/all/#/console: Anchor '/console' not found
buildbots.rst:209: [broken] http://buildbot.python.org/all/waterfall?category=custom.stable&category=custom.unstable: 404 Client Error: Not Found for url: http://buildbot.python.org/all/waterfall?category=custom.stable&category=custom.unstable
buildslave.rst:26: [broken] http://buildbot.python.org/all/buildslaves: 404 Client Error: Not Found for url: http://buildbot.python.org/all/buildslaves
buildslave.rst:188: [broken] http://buildbot.python.org/all/buildslaves: 404 Client Error: Not Found for url: http://buildbot.python.org/all/buildslaves
buildslave.rst:202: [broken] http://docs.buildbot.net/current/manual/cfg-buildslaves.html#latent-buildslaves: Anchor 'latent-buildslaves' not found

I can go through and update all of these references, as well as updating the documentation itself for s/slave/worker/g.

I would also like to rename the file itself to buildworker.rst if that is alright with you.

Assuming this is all good, PR incoming in the next day or two.

[zware]

All of those updates sound good. Let me know if you have trouble finding a link that linkcheck likes on buildbot.python.org; we can try adding redirects if needed.

Any other things that look out of date for Buildbot 0.9.x as you're making those changes, please feel free to fix. I haven't had a chance to look through the page again myself to point out anything else in particular.

I look forward to reviewing your PR :)

[zware]

Thanks @levlaz!