Fixed the library imports for tests on Windows platform

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Related tickets | 
| License       | GNU GPL v3

The `SD_SRC` directory a cygwin path and so not compatible with the
Windows Python executable.

To support running tests on Windows plaform through make.

   $ make test PYTHON=<python executable>

We need an alternative way to add the `SD_SRC` directory into the
Python system path. So we need to change the current working
directory to `SD_SRC`.