When Source_Dirs is set to a regex that matches multiple directories,
such as src/**, it is possible for the same source to appear in different
directories.
The error message has been updated to reflect this scenario.
Issue: eng/gpr/gpr-issues#755
Several tests required their directory names to remove trailing dashes
from their output. Due to changes in the directory structure,
these names were no longer correct.
Additionally, some test names have been made more descriptive,
as simple names like "1" or "2" were no longer suitable for handling
the trailing dash removal.
Also, make some test names more explicit, as tests like "1", or "2" were
not complex anymore to let the trailing dash removal work
