Add the optional feature to specify module_path using mosquitto config

[viraja1]

Optional feature to specify module_path using mosquitto config. If mosquitto broker is run using service, then PYTHONPATH is not available. e.g. sudo service mosquitto start. The service removes all environment variables including PYTHONPATH.

[mbachry]

My gripe with PySys_SetPath is that it replaces sys.path completely with new value. It's unintuitive for any user used to PYTHONPATH environment variable, which extends default path instead of replacing it. A C version of following code would be preferable:

import sys
sys.path.insert(0, data->module_path.split(':'))

If you feel like implementing it, then go ahead. Otherwise, ping me and I'll merge your PR and add my own fix on top of it.

[danielfaust]

Relacing PySys_SetPath(data->module_path);

with

PyObject *sys = PyImport_ImportModule("sys");
PyObject *path = PyObject_GetAttrString(sys, "path");
PyList_Append(path, PyString_FromString(data->module_path));

yields the result you're after.

I got that code from here https://stackoverflow.com/a/8859538/277267 and checked if it works

/ # mosquitto -c /mosquitto/config/mosquitto.conf
1547320203: mosquitto version 1.5.5 starting
1547320203: Config loaded from /mosquitto/config/mosquitto.conf.
1547320203: plugin_init (opts: ((u'pyauth_module_append_path', u'/mosquitto/scripts'),))
['/usr/lib/python27.zip', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/pyt hon2.7/lib-dynload', '/usr/lib/python2.7/site-packages', '/mosquitto/scripts']