When building kolla-ansible image, it clones ansible source code from
github. Since we just need the source code but not the commit history,
there is no need to download all the commit log objects. This patch adds
"--depth 1" option to git clone command. This will speedup kolla-ansible
image building a lot, especially in countries with slow Internet access.
Change-Id: I834f83a127350415a5861a2f5b2982df3d3e3f5a
Closes-Bug: #1488744
32d48e6fb7