In bindep we specify we need GCC to compile deps and set tags to compile
and test as appropriate as none of these packages are needed as runtime
dependencies. In requirements.txt we unpin alembic and beaker and add
PyMySQL. Alembic and beaker need to be unpinned to work with modern
python3 and PyMySQL is a python only runtime dep if using MySQL.
This makes building docker images much simpler.
As it was announced  global bindep-fallback.txt was removed and now
projects need to have a local bindep.txt to be able to install binary
dependencies for testing.
In test jobs the script tools/test-setup.sh is called which requires
mysql and postgres servers and clients to be installed.
To eliminate 'ERROR: InterpreterNotFound: python3.5' of the zuul job
refstack-tox-py35-func-mysql, simply replace the tox environment
py35-func-mysql to py36-func-mysql with a base python of 3.6 instead of
3.5 and rename the zuul job to contain py36 in the name.
Update the Zuul template to use nodejs6 jobs, this makes the single jobs
obsolete, remove them. Without this change, the gate will use
nodejs4 and fail.