Issue #4400 - Review HttpClient's ContentProvider.

Review updates.
Closing MultiPartRequestContent before sending it.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-osgi/test-jetty-osgi/src/test/java/org/eclipse/jetty/osgi/test/TestJettyOSGiBootWithAnnotations.java

@@ -47,7 +47,6 @@ import static org.ops4j.pax.exam.CoreOptions.systemProperty;
  * top of this.
  */
 @RunWith(PaxExam.class)
-
 public class TestJettyOSGiBootWithAnnotations
 {
     private static final String LOG_LEVEL = "WARN";
@@ -135,6 +134,7 @@ public class TestJettyOSGiBootWithAnnotations
             TestOSGiUtil.assertContains("Response contents", content, "<h1>FRAGMENT</h1>");
             MultiPartRequestContent multiPart = new MultiPartRequestContent();
             multiPart.addFieldPart("field", new StringRequestContent("foo"), null);
+            multiPart.close();
             response = client.newRequest("http://127.0.0.1:" + port + "/multi").method("POST")
                 .body(multiPart).send();
             assertEquals(HttpStatus.OK_200, response.getStatus());

jetty-webapp/src/test/java/org/eclipse/jetty/webapp/HugeResourceTest.java

@@ -267,6 +267,7 @@ public class HugeResourceTest
         Path inputFile = staticBase.resolve(filename);
         String name = String.format("file-%d", expectedSize);
         multipart.addFilePart(name, filename, new PathRequestContent(inputFile), null);
+        multipart.close();
 
         URI destUri = server.getURI().resolve("/multipart");
         client.setIdleTimeout(90_000);