plugin: Check source package's name also for multiple whitelist entries

This patch is prework for supporting unit test of other plugins on Windows.

Unlike *nix build which create registry per test case,
we don't create that for Windows, and eventually plugin scanner will
check whether a plugin belongs to whitelist or not.

As an example of failure, coreelement's corresponding GstPluginDesc
stores "source" as "gstreamer" and "name" as "coreelement".
Then, if a unit test set whitelist to "gstreamer,gst-plugins-base",
the "name" (coreelement in this case) never be matched with
"gstreamer" and finally the coreelement plugin couldn't be loaded.
6 jobs for fix-plugin-whitelist in 28 minutes and 57 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #64290
gst indent

00:00:31

passed #64289
manifest

00:00:18

 
  Build
passed #64291
build fedora x86_64

00:02:41

 
  Test
passed #64292
check fedora

00:15:42

 
  Full Builds
passed #64293
build android arm64 api28

00:02:29

passed #64294
build cerbero fedora x86_64

00:09:48