Switch to build-openstack-infra-sphinx-docs for doc build jobs

Exercise the infra version of the job, rather than the one that uses the
non-standard docs environment.

Depends-On: I15fce2938222166e75984b75c568fa0fc083a8ee
Change-Id: Ic075a4e1ea434b3770db7d7e62b0738b13f1b333
1 file changed