Fix generics ambiguity

Inline the method to use concrete subtypes of AbstractBuild to remove ambiguity

```
[INFO] Jenkins war ........................................ SUCCESS [04:19 min]
[INFO] Tests for Jenkins core ............................. FAILURE [ 18.740 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 06:01 min
[INFO] Finished at: 2017-03-29T23:07:16+02:00
[INFO] Final Memory: 92M/504M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.0:testCompile (default-testCompile) on project test: Compilation failure
[ERROR] /home/tiste/dev/JENKINS/jenkins/test/src/test/java/hudson/model/GetEnvironmentOutsideBuildTest.java:[89,30] error: no suitable method found for buildAndAssertSuccess(AbstractProject)
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
[ERROR]
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <goals> -rf :test
```

test/src/test/java/hudson/model/GetEnvironmentOutsideBuildTest.java

@@ -6,8 +6,10 @@ import static org.junit.Assert.assertNull;
 import java.io.IOException;
 
 import hudson.EnvVars;
+import hudson.matrix.MatrixBuild;
 import hudson.matrix.MatrixProject;
 import hudson.maven.MavenModuleSet;
+import hudson.maven.MavenModuleSetBuild;
 import hudson.tasks.Maven.MavenInstallation;
 import hudson.util.StreamTaskListener;
 
@@ -69,24 +71,23 @@ public class GetEnvironmentOutsideBuildTest extends HudsonTestCase {
     public void testMaven() throws Exception {
         MavenModuleSet m = createSimpleMavenProject();
 
-        assertGetEnvironmentCallOutsideBuildWorks(m);
+        final MavenModuleSetBuild build = buildAndAssertSuccess(m);
+
+        assertGetEnvironmentWorks(build);
     }
 
     public void testFreestyle() throws Exception {
         FreeStyleProject project = createFreeStyleProject();
 
-        assertGetEnvironmentCallOutsideBuildWorks(project);
+        final FreeStyleBuild build = buildAndAssertSuccess(project);
+
+        assertGetEnvironmentWorks(build);
     }
 
     public void testMatrix() throws Exception {
         MatrixProject createMatrixProject = jenkins.createProject(MatrixProject.class, "mp");
 
-        assertGetEnvironmentCallOutsideBuildWorks(createMatrixProject);
-    }
-
-    @SuppressWarnings({"rawtypes", "unchecked"})
-    private void assertGetEnvironmentCallOutsideBuildWorks(AbstractProject job) throws Exception {
-        AbstractBuild build = buildAndAssertSuccess(job);
+        final MatrixBuild build = buildAndAssertSuccess(createMatrixProject);
 
         assertGetEnvironmentWorks(build);
     }