PROTON-2086: Fix small errors in python sphinx doc build process - Actually need both sphinx and sphinx_automodapi for doc generation - There was an error in the cmake code if sphinx wasn't detected   We don't need a specific message telling us the python version tried as it   will always be the python version detected earlier by CMake.
PROTON-2086: Fix small errors in python sphinx doc build process
- Actually need both sphinx and sphinx_automodapi for doc generation
- There was an error in the cmake code if sphinx wasn't detected
  We don't need a specific message telling us the python version tried as it
  will always be the python version detected earlier by CMake.

gemmellr/qpid-proton,kgiusti/qpid-proton,kgiusti/qpid-proton,apache/qpid-proton,apache/qpid-proton,ssorj/qpid-proton,astitcher/qpid-proton,ssorj/qpid-proton,ssorj/qpid-proton,gemmellr/qpid-proton,astitcher/qpid-proton,apache/qpid-proton,astitcher/qpid-proton,kgiusti/qpid-proton,gemmellr/qpid-proton,kgiusti/qpid-proton,kgiusti/qpid-proton,ChugR/qpid-proton,ChugR/qpid-proton,astitcher/qpid-proton,ChugR/qpid-proton,gemmellr/qpid-proton,ssorj/qpid-proton,ChugR/qpid-proton,ssorj/qpid-proton,ssorj/qpid-proton,gemmellr/qpid-proton,apache/qpid-proton,apache/qpid-proton,apache/qpid-proton,ChugR/qpid-proton,astitcher/qpid-proton,ChugR/qpid-proton,gemmellr/qpid-proton,astitcher/qpid-proton,kgiusti/qpid-proton