Shallow git clone for better performance

Do not download the entire commit history from the remote.  Execute the
equivalent of `git clone --depth 1`

Fixes spring-cloud#1544

spring-cloud-config-server/src/main/java/org/springframework/cloud/config/server/environment/JGitEnvironmentRepository.java

@@ -77,6 +77,7 @@
  * @author Ryan Lynch
  * @author Gareth Clay
  * @author ChaoDong Xi
+ * @author Chin Huang
  */
 public class JGitEnvironmentRepository extends AbstractScmEnvironmentRepository
 		implements EnvironmentRepository, SearchPathLocator, InitializingBean {
@@ -652,7 +653,7 @@ private Git copyFromLocalRepository() throws IOException {
 
 	private Git cloneToBasedir() throws GitAPIException {
 		CloneCommand clone = this.gitFactory.getCloneCommandByCloneRepository().setURI(getUri())
-				.setDirectory(getBasedir());
+				.setDirectory(getBasedir()).setDepth(1);
 		configureCommand(clone);
 		try {
 			return clone.call();
@@ -772,7 +773,7 @@ public Git getGitByOpen(File file) throws IOException {
 		}
 
 		public CloneCommand getCloneCommandByCloneRepository() {
-			CloneCommand command = Git.cloneRepository().setCloneSubmodules(cloneSubmodules);
+			CloneCommand command = Git.cloneRepository().setCloneSubmodules(cloneSubmodules).setDepth(1);
 			return command;
 		}