broken ceph docs on PRs
Because the build-doc is installing `breathe` from master, which isn't compatible with the Sphinx version it requires (1.6.3)
This causes builds to fail with:
Exception occurred: File "/home/jenkins-build/build/workspace/ceph-pr-docs/build-doc/virtualenv/src/breathe/breathe/renderer/sphinxrenderer.py", line 80, in DomainDirectiveFactory 'union': (cpp.CPPUnionObject, 'union'), AttributeError: 'module' object has no attribute 'CPPUnionObject'
Pinning to version 4.11.1 on breathe would suffice to fix this problem, however, this issue: https://github.com/michaeljones/breathe/issues/416 is tracking the
changes needed in Breathe to correctly require the minimum Sphinx version needed.
The fix means we need to pin the release of breathe in luminous (and Mimic) to the latest released version of breathe (4.11.1) which doesn't have this problem