[scancode] Use scancode from python3 interface

[valeriocos]

Recently scancode has been ported to Python 3, thus the corresponding analyzer could be updated to call scancode using a python interface instead of a system call.

After talking with @pombredanne, there are some minor fixes to be done on scancode which should be included in the upcoming release.

[Dev10-sys]

Thanks for opening this issue.
Before attempting an implementation, I’d like to confirm whether this is still relevant with the current scancode-toolkit Python API.

Is the expected goal here to:

• Replace the CLI-based scancode invocation with direct Python API usage, or
• Support both CLI and Python interfaces conditionally?

I can investigate the current scancode Python interface and propose a minimal update or documentation clarification if this is still desired.