kpm - extra slash in default org.killbill.billing.plugin.kpm.nexusUrl

[xsalefter]

Originally reported here.

Now, AFAIR, this property is a fallback property. But I don't remember why it need to have extra / (that causing bug). Maybe try to comply with previous version?

Nevertheless, current/default state of configuration causing bug explained above, and it need to be fixed. Things that need to do:

1. After all, constructed URL https://oss.sonatype.org//content/ .... is wrong. It should be construct valid URL.
2. Removing extra / in default value seems make sense, but do check thoroughly it not break anything else.
3. Implements this comment.
4. While working at this: Use consistent naming URI vs URL.

[pierre]

Related: #156 ?

[xsalefter]

Solved by this previous PR.

[xsalefter]

Re-open this. I think the fix mentioned by Pierre not covering all problem (see this, or this).

I think we can make this better by:

1. Define how URL (nexusUrl, and maybe others). should looks like. Add this in README.md or CONFIGURATION.md. For example, it should not end with /: http://sonatype.org and https://repo.maven.org/maven2 is valid but https://repo.maven.org/maven2/ is not.
2. Validate point 1, in the first time KpmProperties loaded/constructed.
3. Changes related code to follow this rule (in this case, fix UrlResolverFactory lines as pointed in first paragraph).

[xsalefter]

Fixed by this PR.