Preserve custom PomFile and deployToLocal through var expansion

[copart-jafloyd]

I tried to use the Pom File setting on an artifact, but it had no effect.

The TokenExpander.expand method is the source of the bug because it does not preserve/copy the user-provided pomFile value. In fixing that, I also noticed that deployToLocal was also not preserved, so I included that as well.

The custom pom file feature was introduced in #43 with 2.0.0, but it looks like the var expansion feature was added after the pomFile feature, so the pomFile was inadvertently missed.

There are no Jira or GitHub issues for this afaik.

Testing done

I just installed and successfully tested this build in my Jenkins instance: https://ci.jenkins.io/job/Plugins/job/repository-connector-plugin/job/PR-61/2/artifact/target/repository-connector.hpi In my test, the custom pom file was deploted correctly.

I added some basic unit tests for TokenExpander. Note that I did not test actual var expansion; I only tested that vars are preserved.

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