Decentralize the zuul jobs into zuul.d

Current .zuul.yaml file has 36 jobs definition and
it is growing more which makes it hard to read and
error prone.

This commit move the jobs definitions to zuul.d directory to
different yaml files:
- base.yaml includes base jobs definition
- integrated-gate.yaml includes integrated jobs to be
  used in other openstack projects too.
- stable-jobs.yaml includes all stable jobs
- tempest-specific.yaml includes jobs supposed to run on Tempest
  gate only
- project.yaml includes different pipelines (check, gate etc) definition

Change-Id: I984ecee81a9730b663764800f604333f28fd8180
6 files changed