[MNG-6797] - Remember if Maven model problems were encountered.

[wilx]

Remember in MavenSession if Maven model problems were detected in DefaultGraphBuilder.

The reason for this is to be able to read the problems flag in Maven Enforcer plugin rule that would stop build if any Maven model problems were encountered.

See also MNG-6797.

Following this checklist to help us incorporate your contribution quickly and easily:

• [x] Make sure there is a JIRA issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a JIRA issue. Your pull request should address just this issue, without pulling in other changes.
• [x] Each commit in the pull request should have a meaningful subject line and body.
• [x] Format the pull request title like [MNG-XXX] - Fixes bug in ApproximateQuantiles, where you replace MNG-XXX with the appropriate JIRA issue. Best practice is to use the JIRA issue title in the pull request title and in the first line of the commit message.
• [x] Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• [x] Run mvn clean verify to make sure basic checks pass. A more thorough check will be performed on your pull request automatically.
• [ ] You have run the Core IT successfully.

If your pull request is about ~20 lines of code you don't need to sign an Individual Contributor License Agreement if you are unsure please ask on the developers list.

To make clear that you license your contribution under the Apache License Version 2.0, January 2004 you have to acknowledge this by using the following check-box.

• [x] I hereby declare this contribution to be licenced under the Apache License Version 2.0, January 2004

• [ ] In any other case, please file an Apache Individual Contributor License Agreement.