assert_reference_unique.sh does not discard trailing spaces

[ggbecker]

Description of problem:

assert_reference_unique.sh considers trailing whitespaces as part of the identifiers and sometimes it can lead that two identical identifiers are not properly identified.

The test needs to be updated to discard any trailing space from the extracted identifier before doing the comparison.

Here is a case of identifiers that had trailing space and caused problems:

content/linux_os/guide/system/network/network-uncommon/kernel_module_dccp_disabled/rule.yml

Line 22 in 3b7c651

cce@sle12: CCE-83055-4

[ggbecker]

It appears we have many trailing whitespaces across the project

for example:
find . -type f -name 'shared.xml' -exec sed --in-place 's/[[:space:]]\+$//' {} \+
find . -type f -name '*.yml' -exec sed --in-place 's/[[:space:]]\+$//' {} \+

We should consider adding some kind of tests to prevent that in PR, for example: https://github.com/marketplace/actions/find-trailing-whitespace

It's probably a good idea to remove all trailing whitespaces at once, but that will bring a lot of changes to multiples files ;(