[MNG-8047] Improve aggregator projects support

**[Guillaume Nodet](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=gnt)** opened **[MNG-8047](https://issues.apache.org/jira/browse/MNG-8047?redirect=false)** and commented

Some things are broken in aggregator projects (such as https://github.com/apache/maven-sources/, projects that aggregate multiple projects):

  * the project local repository is different when building the whole or when using `--f` option
  * the `--resume` option should also work on the whole aggregated reactor

maybe more ?

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**Issue Links:**
- [MNG-8162](https://issues.apache.org/jira/browse/MNG-8162) Maven should warn about modules relative to parent directory

Start by reproducing the issue with an aggregator project such as maven-sources, comparing a whole build with one using the --f option. Investigate how the project local repository differs and how --resume handles the aggregated reactor. Done means consistent repository behavior and working resume support across the whole reactor.

Written by the indexing model from the issue text.