Switch zuul jenkins jobs config to use the python jobs template. The
gate-zuul-pyflakes job has been kept though. Add zuul-docs job as well.
Configure the zuul layout to gate zuul on python26 and python27 jobs.
Also configured to run the zuul-coverage job and zuul-docs job post
merge.
Change-Id: Ib3500c361bca0e2c35fa9552b0aa98468d2f040f