Start to replace direct call to master.db with master.data in
  - master/buildbot/process/builder.py
  - master/buildbot/process/build.py

Fix:
 - buildbot/process/buildstep.py
   The return of self.master.data.updates.newStep is a tuple of 3 elems
 - 2 inserts for the same build (but the fix is "ugly", I set Build::buildid to -1 in order to have the unittest pass)