[regression] Invocation of just installed plugin on its plugin project can fail with ComponentLookupException for mojo class

This is a side effect of my initial solution for MNG-3043: Basically, reactor resolution is too eager and resolves artifacts from project output even if the project has not been build in the current reactor build. In other words, a possibly cleaned (but not deleted) output directory is used for the artifact instead of the file from the repo.

For instance, the following steps on a simple plugin project will fail

• mvn install to install the plugin JAR locally
• erasing the contents of the project's target/classes directory, but leaving the directory itself existent
• mvn the-just-installed-plugin:goal
  The last invocation will resolve the plugin from its own invalidate output directory.