Add post docs job for os-cloud-config

It turns out when I71045243e35045483c3c8163f12f7ae6238d00f4 landed,
os-cloud-config no longer ran docs jobs during 'post', which I
thought was okay, since the 'gate' docs job would publish them. It
turns out it does not, so add it back.

Change-Id: Iae6e25668f8f858d4ee3af7fe0dbd61a04674627