Provide support for cloudkitty dev mode in kolla

Add a possibility to mount sources as volumes to containers,
in "more than documentation" way. That will let us to use kolla
as a replacement for devstack.

Partially implements: blueprint mount-sources
Co-Authored-By: ZhijunWei <wzj334965317@outlook.com>

Change-Id: I8ccfb3c96e642d4b121809236aab0180ac49e3cc