[FIX] Discovery middleware shouldn't fail when lib names overlap

[codeworrior]

When a library's name is a prefix of another library's name (like with
sap.m and sap.me), the discovery service mistakenly assigned test pages
to both libraries.

By including the slash in the prefix check, only full segment matches
will be taken into account.

By checking the prefixes from longest to shortest and by aborting after
the first match, non-prefix-free lib names can be handled properly. The
longest matching prefix will win and there won't be double assignments.

Thank you for your contribution! 🙌

To get it merged faster, kindly review the checklist below:

Pull Request Checklist

• Reviewed the Contributing Guidelines
  • Especially the How to Contribute section
• No merge commits
• Correct commit message style

[coveralls]

Coverage increased (+0.01%) to 93.506% when pulling 7e48e73 on fix-discovery into d9a3ce6 on master.

[svbender]

Looks good!

[RandomByte]

What's the priority of this? Should be release it rather quickly?

[codeworrior]

@RandomByte from my POV not urgent. Just stumbled upon redundant entries in the testsuite app's tree when running it in a scope where sap.m and sap.me both are present. But all entries can be found and executed, so it's not a functional issue.