Use the main project to let bnd compute the output file

Currently we compute the name of the subjar manually, but this can be
overridden by the user so it is better to let bnd calculate the file
itself. Additional init the global driver property of workspace.

tycho-bnd-plugin/src/main/java/org/eclipse/tycho/bnd/mojos/BndBuildMojo.java

@@ -49,9 +49,8 @@ protected void execute(Project project) throws Exception {
 				getLog().info(String.format("Building sub bundle '%s'", subProject.getName()));
 				Jar jar = builder.build();
 				checkResult(builder, project.getWorkspace().isFailOk());
-				String jarName = jar.getName();
 				String name = subProject.getName();
-				File file = new File(mavenProject.getBuild().getDirectory(), String.format("%s.jar", jarName));
+				File file = project.getOutputFile(builder.getBsn(), builder.getVersion());
 				file.getParentFile().mkdirs();
 				jar.write(file);
 				helper.attachArtifact(mavenProject, "jar", name, file);

tycho-bnd-plugin/src/main/java/org/eclipse/tycho/bnd/mojos/BndInitMojo.java

@@ -33,6 +33,8 @@
 import org.apache.maven.plugins.annotations.Parameter;
 import org.apache.maven.project.MavenProject;
 
+import aQute.bnd.build.Workspace;
+
 @Mojo(name = "initialize", defaultPhase = LifecyclePhase.INITIALIZE)
 public class BndInitMojo extends AbstractMojo {
 
@@ -74,6 +76,7 @@ public class BndInitMojo extends AbstractMojo {
 
 	@Override
 	public void execute() throws MojoExecutionException, MojoFailureException {
+		Workspace.setDriver("maven-tycho");
 		fixupPolyglot();
 		writeConsumerPom();
 	}