Error in getting package licenses for node image with scancode

[nishakm]

Describe the bug
Traceback when running tern with scancode on node image with the default report

To Reproduce

1. Install tern and scancode in a development environment
2. Run tern report -i node:16-slim -x scancode -o output.txt
3. See error

Error in terminal

2021-06-11 11:58:43,468 - DEBUG - generator - Creating a detailed report of components in image...
Traceback (most recent call last):
  File "/home/nisha/terndev/bin/tern", line 10, in <module>
    sys.exit(main())
  File "/home/nisha/terndev/tern/tern/__main__.py", line 286, in main
    do_main(args)
  File "/home/nisha/terndev/tern/tern/__main__.py", line 116, in do_main
    crun.execute_image(args)
  File "/home/nisha/terndev/tern/tern/analyze/default/container/run.py", line 90, in execute_image
    report.report_out(args, full_image)
  File "/home/nisha/terndev/tern/tern/report/report.py", line 95, in report_out
    report = generate_report(args, *images)
  File "/home/nisha/terndev/tern/tern/report/report.py", line 52, in generate_report
    return generate_format(images, 'default', args.print_inclusive)
  File "/home/nisha/terndev/tern/tern/report/report.py", line 65, in generate_format
    return mgr.driver.generate(images, print_inclusive)
  File "/home/nisha/terndev/tern/tern/formats/default/generator.py", line 144, in generate
    return report + print_licenses_only(image_obj_list)
  File "/home/nisha/terndev/tern/tern/formats/default/generator.py", line 124, in print_licenses_only
    full_license_list = content.get_licenses_only(image_obj_list)
  File "/home/nisha/terndev/tern/tern/report/content.py", line 40, in get_licenses_only
    pkg_licenses = get_layer_packages_licenses(layer)
  File "/home/nisha/terndev/tern/tern/report/content.py", line 19, in get_layer_packages_licenses
    package_licenses = get_package_licenses(package)
  File "/home/nisha/terndev/tern/tern/report/content.py", line 54, in get_package_licenses
    pkg_licenses.add(package.pkg_license)
TypeError: unhashable type: 'list'

Expected behavior
This should execute successfully

[abhaykatheria]

@nishakm @rnjudge The error in issues #982 and #844 is also same, i think its the way scancode is adding packages is resulting in these kind of errors.

[rnjudge]

Scancode will sometimes report the declared_license value from the package dictionary as a list (of strings OR dicts) which is causing this error. Tern just needs to be able to translate the list value(s) into a concatenated string. I will submit a PR for this fix shortly.