Forcefully init the OSGi system due to p2 issue

See eclipse-equinox/p2#439
Fix #3437

(cherry picked from commit 87563c6)

p2-maven-plugin/src/main/java/org/eclipse/tycho/p2maven/transport/Java11HttpTransportFactory.java

@@ -23,6 +23,7 @@
 import java.net.http.HttpClient.Redirect;
 import java.net.http.HttpClient.Version;
 import java.net.http.HttpRequest;
+import java.net.http.HttpRequest.BodyPublishers;
 import java.net.http.HttpRequest.Builder;
 import java.net.http.HttpResponse;
 import java.net.http.HttpResponse.BodyHandlers;
@@ -156,7 +157,8 @@ private HttpResponse<InputStream> performGet() throws IOException, InterruptedEx
 		public Response<Void> head() throws IOException {
 			try {
 				HttpResponse<Void> response = client.send(
-						builder.method("HEAD", null).timeout(Duration.ofSeconds(TIMEOUT_SECONDS)).build(),
+						builder.method("HEAD", BodyPublishers.noBody()).timeout(Duration.ofSeconds(TIMEOUT_SECONDS))
+								.build(),
 						BodyHandlers.discarding());
 				return new ResponseImplementation<>(response) {
 					@Override

tycho-its/projects/tycho-p2-director-plugin/director-goal-standalone/pom.xml

@@ -0,0 +1,34 @@
+<project
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>foo</groupId>
+  <artifactId>bar</artifactId>
+  <version>0.1.0-SNAPSHOT</version>
+  <packaging>pom</packaging>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.eclipse.tycho</groupId>
+        <artifactId>tycho-p2-director-plugin</artifactId>
+        <version>${tycho-version}</version>
+        <executions>
+          <execution>
+            <id>run-director</id>
+            <goals>
+              <goal>director</goal>
+            </goals>
+            <phase>package</phase>
+            <configuration>
+              <repositories>${target-platform}</repositories>
+              <installIUs>org.eclipse.osgi</installIUs>
+              <destination>target/dummy</destination>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+
+</project>

tycho-its/src/test/java/org/eclipse/tycho/test/P2DirectorPluginTest.java

@@ -0,0 +1,15 @@
+package org.eclipse.tycho.test;
+
+import org.apache.maven.it.Verifier;
+import org.junit.Test;
+
+public class P2DirectorPluginTest extends AbstractTychoIntegrationTest {
+
+	@Test
+	public void testDirectorStandalone() throws Exception {
+		Verifier verifier = getVerifier("tycho-p2-director-plugin/director-goal-standalone", true, true);
+		verifier.executeGoal("package");
+		verifier.verifyErrorFreeLog();
+	}
+
+}

tycho-p2-director-plugin/src/main/java/org/eclipse/tycho/plugins/p2/director/DirectorMojo.java

@@ -38,6 +38,7 @@
 import org.eclipse.equinox.p2.core.IProvisioningAgent;
 import org.eclipse.equinox.p2.core.IProvisioningAgentProvider;
 import org.eclipse.equinox.p2.core.ProvisionException;
+import org.eclipse.equinox.p2.repository.metadata.IMetadataRepositoryManager;
 import org.eclipse.tycho.TargetEnvironment;
 import org.eclipse.tycho.TychoConstants;
 import org.eclipse.tycho.core.shared.StatusTool;
@@ -396,6 +397,8 @@ public void execute() throws MojoExecutionException, MojoFailureException {
         args.addNonNull("-trustedPGPKeys", trustedPGPKeys);
         args.addNonNull("-trustedCertificates", trustedCertificates);
         try {
+            //FIXME forcefully init OSGi unless we have a fix for https://github.com/eclipse-equinox/p2/pull/439
+            agent.getService(IMetadataRepositoryManager.class);
             MavenDirectorLog directorLog = new MavenDirectorLog(execution.getExecutionId(), getLog());
             Object exitCode = new DirectorApplication(directorLog,
                     PhaseSetFactory.createDefaultPhaseSetExcluding(new String[] { PhaseSetFactory.PHASE_CHECK_TRUST }),