recent homebrew changes: python points to python3

Opening this ticket as an FYI to maintainers, and a heads-up to anyone who might be confused by seeing this error. Also hoping to get some tips about how best to work around.

Ran into a build error on carmen-cache, related to python versioning:

$ make
V=1 ./node_modules/.bin/node-pre-gyp configure build --loglevel=error
gyp ERR! configure error
gyp ERR! stack Error: Python executable "/usr/local/bin/python" is v3.6.4, which is not supported by gyp.
gyp ERR! stack You can pass the --python switch to point to Python >= v2.5.0 & < 3.0.0.
gyp ERR! stack     at Object.failPythonVersion 

This is because recent homebrew changes make it so that python points to 3.x instead of 2, as it did before:

On 1st March 2018 the python formula will be upgraded to Python 3.x and a python@2 formula will be added for installing Python 2.7

As the error message says, the --python switch can be used to point to the right Python executable, but it might be tricky to set this in a way that's consistent across environments.

The issue names no files or tests. Start by reproducing make with Homebrew's Python 3 default and inspect the node-pre-gyp/gyp configure entry point; a contribution is not defined until maintainers choose whether compatibility, configuration guidance, or documentation is wanted.