Provide support for kolla dev mode in designate. When
'kolla_dev_mode' or 'designate_dev_mode' variables are
enabled, source code of designate project is cloned
and bindmounted.

Partially implements: blueprint mount-sources
Co-Authored-By: zhulingjie <easyzlj@gmail.com>

Change-Id: Ib23fbd3d5ebc7e3ac372e0db1e0048d333eb95c0