Maybe we should use 'parts +=' everywhere in /components/*/buildout.cfg

lab.nexedi.com is now our main domain for git hosting.
lab.nexedi.cn continues to work for backward-compatibility reasons.

/reviewed-by: TrustMe

also add component/python-PyYAML because cliff 1.15.0 requires PyYAML.

  it includes working wendeling plugin

  Each slave can introduce test parameter to be tested.
  Each slave has a log dedicated folder.

envirionment+= seems not working here.

that is required by serf library, that is required by subversion.
it seems that in some environment this rpath is explicitly required.