python tools can load libs from ~/.local

By default, python (including our packaged cbpy python) will look for libraries in the "user site directory", which on most Unix systems is ~/.local/lib/pythonX.Y/site-packages.  It will load libraries here in preference to those installed in the main python install location. This can lead to binaries like couchbase-cli failing if the local user account has incompatible libraries, which has led to test failures such as described on MB-57308.