set up test requirements with extras_require

Fixes #3060.
Make BuildslaveManager an AsyncMultiService

Without this, slow service starts (e.g., buildslave) can continue on
even after the parent service has indicated it is done starting.  Fixes #3066.
address review comments for NO_INSTALL_REQS
Merge djmitche/buildbot:bug3066 (PR #1399)
Merge pull request #1395 from djmitche/bug3060

set up test requirements with extras_require
rename reconfigService() to reconfigServiceWithBuildbotConfig

In the aim of simplifying the API for BuildbotService(),
we rename this method, so that the name is available for API of BuildbotService.

Next task is to convert more and more services of buildbot into BuildbotService, so that:
1) they can be abstracted from where they are configured
2) they can embed their checkConfig internally, and not in config.py

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
Merge pull request #1394 from tardyp/services

rename reconfigService() to reconfigServiceWithBuildbotConfig

See ticket:3084