[MNG-7667] Fix Bootstrap IT

[cstamas]

This change extends Bootstrap IT (1st IT that fills in local repo) to hunt down some plugins that are bound in lifecycles provided by Maven under test.

Changes:

• the Bootstrap IT invokes only the phase where DownloadMojo is bound
• DownloadMojo (the "bootstrap") changed to do "this or that": it either resolves all artifacts from provided file OR collects plugins for given project packaging plugin versions provided by tested Maven default lifecycle.
• Split more Bootstrap project POMs, now we have 4 modules, we can add more (even extension if needed)

---

https://issues.apache.org/jira/browse/MNG-7667

[cstamas]

This fixes the original issue, but now (with apache/maven#956) we face other issue: all the ITs that use maven-plugin packaging and do verifier.verifyErrorFreeLog will fail, as m-plugin-p emits ERRORs that should be WARNs instead...

Example:

[INFO]
[INFO] --- plugin:3.7.0:descriptor (default-descriptor) @ plugin-extension ---
[ERROR]

Some dependencies of Maven Plugins are expected to be in provided scope.
Please make sure that dependencies listed below declared in POM
have set '<scope>provided</scope>' as well.

The following dependencies are in wrong scope:
 * org.apache.maven:maven-model:jar:3.8.6:compile
 * org.apache.maven:maven-artifact:jar:3.8.6:compile
 * org.apache.maven:maven-resolver-provider:jar:3.8.6:compile
 * org.apache.maven:maven-model-builder:jar:3.8.6:compile
 * org.apache.maven:maven-builder-support:jar:3.8.6:compile
 * org.apache.maven:maven-repository-metadata:jar:3.8.6:compile



[INFO] Using 'UTF-8' encoding to read mojo source files.
[INFO] java-annotations mojo extractor found 0 mojo descriptor.
[INFO] java-javadoc mojo extractor found 1 mojo descriptor.
[WARNING]
[WARNING] Deprecated extractor java-javadoc extracted 1 descriptor. Upgrade your Mojo definitions.
[WARNING] You should use Mojo Annotations instead of Javadoc tags.
[WARNING]
[INFO] ant mojo extractor found 0 mojo descriptor.
[INFO] bsh mojo extractor found 0 mojo descriptor.
[INFO]
[INFO] --- resources:3.3.0:testResources (default-testResources) @ plugin-extension ---

This is logged as https://issues.apache.org/jira/browse/MPLUGIN-452