Stabilize two test that seem to often fail on the CI

Signed-off-by: azerr <azerr@redhat.com>

Author: angelozerr

org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/extensions/contentmodel/model/ContentModelManager.java

@@ -546,4 +546,8 @@ public void forceDownloadExternalResource(String url) {
 		cacheResolverExtension.forceDownloadExternalResource(url);
 	}
 
+	public void waitForDownload(String resourceUri) {
+		cacheResolverExtension.waitForDownload(resourceUri);		
+	}
+
 }

org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/extensions/contentmodel/uriresolver/XMLCacheResolverExtension.java

@@ -172,4 +172,8 @@ public void evictCache() throws IOException {
 	public void forceDownloadExternalResource(String url) {
 		cacheResourcesManager.forceDownloadExternalResource(url);
 	}
+
+	public void waitForDownload(String resourceUri) {
+		cacheResourcesManager.waitForDownload(resourceUri);
+	}
 }

org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/uriresolver/CacheResourcesManager.java

@@ -31,6 +31,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -492,4 +493,16 @@ public void forceDownloadExternalResource(String url) {
 	private boolean isForceDownloadExternalResource(String url) {
 		return forceDownloadExternalResources.getIfPresent(url) != null;
 	}
+
+	public void waitForDownload(String resourceUri) {
+		CompletableFuture<Path> downloadedFile = resourcesLoading.get(resourceUri);
+		if (downloadedFile != null) {
+			try {
+				downloadedFile.get();
+			} catch (InterruptedException e) {
+				Thread.currentThread().interrupt();
+			} catch (ExecutionException e) {
+			}
+		}
+	}
 }

org.eclipse.lemminx/src/test/java/org/eclipse/lemminx/extensions/contentmodel/XMLValidationExternalResourcesBasedOnDTDTest.java

@@ -83,7 +83,8 @@ public void docTypeDownloadProblem() throws Exception {
 				"<root-element>\r\n" + //
 				"</root-element>";
 
-		String dtdCachePath = CacheResourcesManager.getResourceCachePath("http://localhost:8080/sample.dtd").toString();
+		String resourceUri = "http://localhost:8080/sample.dtd";
+		String dtdCachePath = CacheResourcesManager.getResourceCachePath(resourceUri).toString();
 		String fileURI = "test.xml";
 		// Downloading...
 		XMLAssert.testPublishDiagnosticsFor(xml, fileURI, validation, ls,
@@ -96,8 +97,9 @@ public void docTypeDownloadProblem() throws Exception {
 						new Diagnostic(r(1, 1, 1, 13), "Element type \"root-element\" must be declared.",
 								DiagnosticSeverity.Error, "xml", DTDErrorCode.MSG_ELEMENT_NOT_DECLARED.getCode())));
 
-		TimeUnit.SECONDS.sleep(5); // HACK: to make the timing work on slow machines
-
+		ContentModelManager contentModelManager = ls.getComponent(ContentModelManager.class);
+		contentModelManager.waitForDownload(resourceUri);
+		
 		// Downloaded error
 		XMLAssert.testPublishDiagnosticsFor(xml, fileURI, validation, ls,
 				pd(fileURI,
@@ -164,7 +166,8 @@ public void entityRefDownloadProblem() throws Exception {
 				"	&abcd;\r\n" + //
 				"</root-element>";
 
-		String dtdCachePath = CacheResourcesManager.getResourceCachePath("http://localhost:8080/sample.dtd").toString();
+		String resourceUri = "http://localhost:8080/sample.dtd";
+		String dtdCachePath = CacheResourcesManager.getResourceCachePath(resourceUri).toString();
 		String fileURI = "test.xml";
 		// Downloading...
 		XMLAssert.testPublishDiagnosticsFor(xml, fileURI, validation, ls,
@@ -177,7 +180,8 @@ public void entityRefDownloadProblem() throws Exception {
 						new Diagnostic(r(6, 1, 6, 7), "The entity \"abcd\" was referenced, but not declared.",
 								DiagnosticSeverity.Error, "xml", DTDErrorCode.EntityNotDeclared.getCode())));
 
-		TimeUnit.SECONDS.sleep(5); // HACK: to make the timing work on slow machines
+		ContentModelManager contentModelManager = ls.getComponent(ContentModelManager.class);
+		contentModelManager.waitForDownload(resourceUri);
 
 		// Downloaded error
 		XMLAssert.testPublishDiagnosticsFor(xml, fileURI, validation, ls,