Move most of `basic-build-test.sh` to the framework

[mpg]

Similarly to #86 we want to keep the entry point in each branch for the CI's benefit, but move the bulk of the file to the framework - see #86 for a suggested strategy, with obvious adaptation for shell vs python.

Note that currently the file is not identical between 3.6 and development. However the differences are minor and it looks like just using the version from development will work.