Isolate builds of Boost ITs using invoker plugin

[scottkurz]

Two issues:

1. Made me nervous to realize that this dependency in boost-maven-plugin

   <dependency>
       <groupId>boost</groupId>
       <artifactId>boost-common</artifactId>
       <version>0.1.3-SNAPSHOT</version>
   </dependency>
   

is somehow propagated to the test-compile classpath for the IT build.

I noticed this when I did cd target/it/test-jdbc-db2; mvn install..... and couldn't figure out why test-compile was failing.

It seems we should be more careful about this.. the ITs are important "samples" for us, and we should be able to look at their POMs and see how they build.. and not rely on some other context from the parent build.

I can't find where in the https://maven.apache.org/plugins/maven-invoker-plugin/ doc this behavior comes from actually. So not sure how to quickly turn it off, so let's investigate.

2. On the subject of clean builds...it seems we should at least look into whether to use the recommended: <localRepositoryPath> option instead of falling back to the user's local repo. If the performance isn't much worse it seems like this could avoid a possible debugging headache at some point.