[MNG-6972] allow access to org.apache.maven.graph

[mickroll]

fixes MNG-6972

With this PR, maven extensions can access the GraphBuilder to update the dependency graph after adding dependencies.

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[mickroll]

Failing test:

[ERROR] Tests run: 846, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 256.781 s <<< FAILURE! - in org.apache.maven.it.IntegrationTestSuite
[ERROR] testmng5175_ReadTimeOutFromSettings(org.apache.maven.it.MavenITmng5175WagonHttpTest)  Time elapsed: 0.174 s  <<< ERROR!
org.apache.maven.it.VerificationException: Text not found in log: Could not transfer artifact org.apache.maven.its.mng5175:fake-dependency:pom:1.0-SNAPSHOT
	at org.apache.maven.it.MavenITmng5175WagonHttpTest.testmng5175_ReadTimeOutFromSettings(MavenITmng5175WagonHttpTest.java:128)

Can't see why this fails for the change in this PR.

Hint: this test runs fine on my machine:

[INFO] Running org.apache.maven.it.MavenITmng5175WagonHttpTest
58 [main] INFO org.eclipse.jetty.server.Server - jetty-9.0.4.v20130625
152 [main] INFO org.eclipse.jetty.server.ServerConnector - Started ServerConnector@7d900ecf{HTTP/1.1}{0.0.0.0:60411}
Bound server socket to the port 60411
mng5175 WagonHttp.mng5175_ReadTimeOutFromSettings().......... OK (2.5 s)
2697 [main] INFO org.eclipse.jetty.server.ServerConnector - Stopped ServerConnector@7d900ecf{HTTP/1.1}{0.0.0.0:0}
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.893 s - in org.apache.maven.it.MavenITmng5175WagonHttpTest

[michael-o]

It is probably ephemeral.

[mickroll]

Added integration test: apache/maven-integration-testing#69

[michael-o]

Looks OK to me. @rfscholte IT is fine too. Any objections?

[rfscholte]

LGTM